Your list is basically the custom lineage from Tasha with a few additional options.
Please be aware I'm not against a custom lineage race, but I don't think that is what people will want when they make a firbolg/drow crossbreed. It might be no better than "pick one and reflavor" because you at least get the major features of one of your two parents.
we can try to give point value to racial features:
Pick your racial traits;
you have 6/7 trait points:
skill proficiency, max 2 times
combination of 4 tools, languages and/or weapons, max 2 times
expertise in one racial tool or skill
darkvision 60ft
darkvision 120ft, worth 2 points
hardy: +2 HP, +1 HP for every level after 1st, worth 2 pts
damage type resistance(except bludgeoning, slashing or piercing), max 2 times
healthy: advantage and resistance vs poison and disease
durable: advantage on one saving throw
+5 move speed, max 2 times
climb speed equal to move speed
swim speed equal to move speed and hold breath 1hr
burrow speed, half your speed
fly speed(wings), worth 4 points
cantrip, max 2 times
one level 1 spell known, cast for free once per long rest
one level 2 spell known, cast for free once per long rest
one level 3 spell known, cast for free once per long rest, worth 2 points
extra feat: worth 5 points
natural armor 13+dex or +1 AC when wearing armor you are proficient
natural weapon 1d6+str or 1d4+dex, one attack as bonus action
large frame: count as one size larger for carry capacity, grappling and similar
Improved ability: +1 ASI, new score cannot be higher than 17. worth 2 points
negative traits:
slow: -5ft speed, gain one trait point
small size: gain one trait point
sunlight sensitivity: gain one trait point
-1 to one ability; gain one trait point, max 2 times, cannot be taken on ability 8 or lower.
now pricing shifters ability or aasimars might be dificult but I would say that by this formula it's worth 2 points
If we put value on every racial feature, then all can be in a budget of 6 or 7 pts.
then when you do a mixed heritage, you just pick from the pool of abilities of both races and watch that you do not go over budget.