At the end of the day, its all about flexibility vs complexity. 2 levels of feats is easier but limits the amount of flexibility, 6 levels of much more flexible but more complicated.
What is the best number: 2, 4, 6.... not sure. Considering that level up is going for more crunch, this seems like a decent place to look. It provides a lot more options, but the crunch is done during "level up" (see what I did there
, so its not that you are greatly increasing the complexity of running the game. That to me is the best kind of added complexity, so I am on board with the concept.
As I'm reading through the list (I ignored the racial ones for the moment), my notes. In general I like everything I did not comment on, it could be easy to think I'm being critical looking at this long list, but there is a lot I didn't comment on because I thought it was ready to rock.
Close Quarters Shooter vs Crossbow Expert: I would generally rank the later ability higher than the former.
Duel Wielder: I feel in the spirit of other feats you have broken up you could do the same here.
Durable: My table generally thinks this feat is pretty weak, so I would recommend 3 pts for it.
Elemental Adapt: A lot of people don't like the idea of negating immunities. My fire is so hot I burn fire elementals. I would make this a cheaper feat that just ignores the resistance.
Armor Proficiencies: I would prefer just one feat that combines these together. Aka a feat you can take up to 3 times and it raises your level of proficiency by 1 each time. Also, I think the strength prereqs are too high. I don't mind so strength needed, but a 16 for heavy armor? A lot of NPC warriors may not have those numbers.
Inspiring Leader: This is a strong feat normally that my table has used often. This one feels like a 6 pt to me.
Mage Slayer: This is a good full feat in the base game. Now you took away the save bonus which is a thing, but I think this is still worth at least 4 pts.
Magic Initiate: Another good full feat in the base game. Cantrips are the best part of the feat (the 1st level spell is nice but at will casting you will get much more mileage out of. I would change this to 4 pts.
Martial Adept: That last sentence is a bit confusing, could just use some language cleanup.
Observant: Should be 4 pts minimum, its a solid feat in the core game.
Polearm Master: When you consider the 5 pt fighting style is basically +2 damage (or less with two handers), adding a +1d6 (aka 3.5 avg) damage for 4 pts seem underpowered. 5 pts at least. Honestly I think this is a bad option, your just pushing bounded accuracy. The vast majority of the other options I have liked because they add flexibility, or if they add power its power within the usual scope. This one just feels like power creep.
Power Attack: What THW user is not going to take this?
Resilent: I think you could go even more granular with this. Make it 3 pts for Str, Int, or Cha save... 4 pts for Dex, Con, or Wis save. We know there is a difference in the save strengths, so we might as well use your granular system for that benefit.
Sentinel: This means I get an OA every time someone moves next to me as written. That's simply too good for a feat, even at 6. I think you could drop this feat to 5 pts, and just have a clause that moving "through" your reach provokes an OA.
Skill Expert: I think this can be 4 pts, heck maybe 5. Expertise is rare in 5e right now, and its special because of its bounded accuracy breaking. Trust me the skill players in my group would still eat that up at a 4.
Tavern Brawler: Unless there is a specific reason you don't want unarmed strikes to interact with finesse benefits, you could just change the language to make unarmed strike finesse weapons. I would also remove the note about making an unarmed strike as a bonus action....players can already do that with TWF...so adding it here I think just muddies the rules waters.
Tool Expertise: Should be no cheaper than Skill Expert, even if the range of useful tools is limited, a good player will still just pick the best tools and get just as much benefit as a skill would.
Warcaster: Should be 6 pts, its already too common imo.
What is the best number: 2, 4, 6.... not sure. Considering that level up is going for more crunch, this seems like a decent place to look. It provides a lot more options, but the crunch is done during "level up" (see what I did there

As I'm reading through the list (I ignored the racial ones for the moment), my notes. In general I like everything I did not comment on, it could be easy to think I'm being critical looking at this long list, but there is a lot I didn't comment on because I thought it was ready to rock.
Close Quarters Shooter vs Crossbow Expert: I would generally rank the later ability higher than the former.
Duel Wielder: I feel in the spirit of other feats you have broken up you could do the same here.
Durable: My table generally thinks this feat is pretty weak, so I would recommend 3 pts for it.
Elemental Adapt: A lot of people don't like the idea of negating immunities. My fire is so hot I burn fire elementals. I would make this a cheaper feat that just ignores the resistance.
Armor Proficiencies: I would prefer just one feat that combines these together. Aka a feat you can take up to 3 times and it raises your level of proficiency by 1 each time. Also, I think the strength prereqs are too high. I don't mind so strength needed, but a 16 for heavy armor? A lot of NPC warriors may not have those numbers.
Inspiring Leader: This is a strong feat normally that my table has used often. This one feels like a 6 pt to me.
Mage Slayer: This is a good full feat in the base game. Now you took away the save bonus which is a thing, but I think this is still worth at least 4 pts.
Magic Initiate: Another good full feat in the base game. Cantrips are the best part of the feat (the 1st level spell is nice but at will casting you will get much more mileage out of. I would change this to 4 pts.
Martial Adept: That last sentence is a bit confusing, could just use some language cleanup.
Observant: Should be 4 pts minimum, its a solid feat in the core game.
Polearm Master: When you consider the 5 pt fighting style is basically +2 damage (or less with two handers), adding a +1d6 (aka 3.5 avg) damage for 4 pts seem underpowered. 5 pts at least. Honestly I think this is a bad option, your just pushing bounded accuracy. The vast majority of the other options I have liked because they add flexibility, or if they add power its power within the usual scope. This one just feels like power creep.
Power Attack: What THW user is not going to take this?
Resilent: I think you could go even more granular with this. Make it 3 pts for Str, Int, or Cha save... 4 pts for Dex, Con, or Wis save. We know there is a difference in the save strengths, so we might as well use your granular system for that benefit.
Sentinel: This means I get an OA every time someone moves next to me as written. That's simply too good for a feat, even at 6. I think you could drop this feat to 5 pts, and just have a clause that moving "through" your reach provokes an OA.
Skill Expert: I think this can be 4 pts, heck maybe 5. Expertise is rare in 5e right now, and its special because of its bounded accuracy breaking. Trust me the skill players in my group would still eat that up at a 4.
Tavern Brawler: Unless there is a specific reason you don't want unarmed strikes to interact with finesse benefits, you could just change the language to make unarmed strike finesse weapons. I would also remove the note about making an unarmed strike as a bonus action....players can already do that with TWF...so adding it here I think just muddies the rules waters.
Tool Expertise: Should be no cheaper than Skill Expert, even if the range of useful tools is limited, a good player will still just pick the best tools and get just as much benefit as a skill would.
Warcaster: Should be 6 pts, its already too common imo.