This is great feedback. Thanks, all. I only have time for a quick response at the moment:
1. Reason for 1 reaction per turn is so that you can't, for example, get a whole bunch of opportunity attacks at once. OP synergy with War Caster.
A whole bunch of OA's at once still doesn't seem bad. It's still a 1 attack for 1 attack trade. So you make 3 attacks a little sooner than otherwise. Possibly make it a move, so it cost a little more.
Warcaster is still something to watch out for...
It's probably best to simply just avoid using the words "Reaction" or "Opportunity Attack", as well as "Move", and avoid all the baggage that comes with them. Instead make a seperate word.
(looks up synonyms...) counter, response, answer, reply, rejoinder, retort, riposte....
Maybe counter measure? Counter step?
You;re spending movement, so "counter step" seems good. At least for the rest of this post.
"You perform a counter step, by trading out one of the following...."
3. I don't love the idea of extending the range of what are really melee range interactions based on INT. That starts to feel, to me, like a return to feeling like magic without being magic.
My justification. The smarter you are, the more you can keep track of, the more you can react to.
A low Int person can only focus on the enemy in front of him. A higher Int person could also follow what's happening to their friend 20' away.
4. That leaves us with uses for Int. I have some ideas but want to flesh them out.
You can tie Int to the counter stepts themselves.
i.e.
When a creature makes an attack, you can give them +Int to their roll.
Hmm... Though I think I prefer advantage.
Maybe knowing more counter steps? So high Int people can cover more
situations, if not more physical area.
You learn a number of counter steps equal to 2+ your intelligence modifer (minimum 1).
Possibly.
So how about at level 3 you are allowed to use movement as part of any reaction, up to your movement rate, deducting it from your movement on your next turn. At level 7 you get 5 'free' feet per reaction, and that increases by 5' at 10, 15, and 18. So that by 18 if you move 30' for your reaction, you only deduct 10' from your total.
I like that.
5. "So Crazy It Just Might Work": I really wanted an ability that represented making a "plan" for the whole party, as opposed to just bestowing a bonus on one person. I have some other variants of this I'll share later.
Fair.
Also, if you go with "counter step" (or whatever), you can just make inititive boosting one of the optoins. Since it's not a "reaction", you can use it durring inititve.
It's true that in general an Action Surge for 1 reaction is a bad trade, especially at higher level...
Maybe space it out?
You can use your Action Surge to gain 3 bonus counter steps. You can use these bonuses counter steps at any time before the end of your next short rest, but only once per round.
At level 20, this increases to 4 counter steps.
Maybe allow for variety?
You can expend your action surge to perform any counter step, including ones you do not know.
Dunno, but it needs something.