I've been playing around with the idea of a homebrew system built where you build your own character class, Mutants and Masterminds style, but built out of a Pathfinder chassis. This is the first time I've ever tried something like this, so I'm not sure if it can even be done without being horribly broken, so I'd appreciate some insight from anyone with actual experience designing a homebrew system.

The idea is that you start by picking a class focus: Combat, Magic or Stealth, which grants you a starting pool for Hit Dice, weapon/armor proficiencies, skills and saves. Then you use some kind of point system to purchase starting class features. Weapon proficiencies use are picked up by choosing fighter weapon groups to be proficient in, rather than simple/martial/exotic. Class features would be classified by Combat, Magic, Stealth or Universal, with Universal class features including things like altering HD per levels or combat styles (like with rangers, but more of them and available to everyone). Universal class features and class features for your class focus cost the same number of points regardless, but taking a class feature from another focus would cost more points to take. For example, it would cost more to take Sneak Attack as a class feature if your focus is combat or magic. During character creation, you would also pick out additional class skills based on your Intelligence modifier. At level up, you would be given additional points for to buy new class features, usually no more than two three, plus the usual compliment of feats and skill points.

For example, say you wanted to play an arcane trickster type with a heavier emphasis on magic. You would choose magic as your focus, which would automatically grant d6 HD, 2+Int skills, one weapon and one armor group to be proficient in, and the Spellcasting class feature. Say that you get get 4 points for class features every level. You'd pick your spells, then choose to take the following class features: Scribe Spell, Additional Weapon Proficiency to get a ranged weapon, and Trap Master to be able to use Disable Device against traps. Scribe Spell is a magic ability and Additional Weapon Proficiency is a universal, costing 1 point apiece. But since Trap Master is a stealth class feature, it costs 2 points to take, and you would have to wait till level 2 to take Sneak Attack.

Or if you wanted to do a paladin-style character and act as the secondary healer, you'd choose the Combat focus, and use Feature points sparingly for a couple of levels to afford Spellcasting to gain access to healing spells.

That's the gist of it thus far for character creation, with the option of saving points from one level to the next to purchase more powerful class features further down the road. Your Focus would also make qualifying for certain feats or progressing through feat trees faster. For instance, someone with the Magic focus would have an easier time qualifying for meta-magic feats, or a Combat-focused character might gain a Feature that lets her perform a free Trip attempt before full attacking and ignore Combat Expertise as a prereq for Improved Trip. Just as an example, as I want to streamline some of the feat trees anyway, and there are a lot of threads about that topic I can search through.

As this is an experiment for right now, I'm welcome to any and all feedback, but here are some issues I'd especially like suggestions for:
- Can something like this work well (or at all) with the Pathfinder system, or am I better off sticking to systems that already allow this level of customization?
- Where to set hard limits for how many features you can take every level.
- Maintaining game balance. As it stands now there isn't any real way to discourage players from tacking spellcasting onto every single character and potentially breaking the game. I've considered making spellcasters choose from a spell list that they have to take their spells from, so no one has access to every spell in the game, but that feels almost like it defeats the purpose of the expanded customization. Plus, I'd like to see pure martial characters being able to hold their own at higher levels. I'd also considered going with a mana-pool style of magic.
- Should I drop feats altogether and increase the amount of features you can take each level, or rework feats to be more like D&D 5e, where they're fewer in number but more powerful?

Thank you for any and all feedback.