Let me try to answer your latest questions.
1. Yes, you got that right, however, the game mechanism is extremely sophisticated. A lot of things will have a certain influence on your Combat Arts, but basically, to level them up, you have to read a rune or wear items with +CA modifiers. As the others stated before me, it is unwise to raise your CA levels too quickly. When I start a new character, I usually won't read a new rune until she passes level 20 (except for a High Elf, but that's another story).
2. To get modification points, you have to raise the level of your lore OR focus skill of the desired Aspect. Or both, of course. You get a modification point to spend each time when the level of the lore and the focus skills reach a certain value (3, 5, 9, 14, 22, 31, 42... etc). Mind you, only hard points count (which you add manually at each new level). On the other hand, weapon-based aspects, like the Malevolent Champion and Death Warrior of the Shadow Warrior, will benefit from raising the focus skill AND Tactics Lore. Please think about Tactics Lore as a general Lore skill for all weapon-based aspects.
Also do not forget that you can raise the effectivity of your Combat Arts by raising the level of their Lore skill, as it will raise their damage, critical chance and casting speed!
3. Each and every Combat Art can be modified three times. You can choose ONE modification each time from the top or the bottom row, and yes, you can mix them as you like. Personally I find these modification issues the hardest choices of the game - I used to reroll characters completely because a wrong decision.
Hopefully this helps!
Enjoy the game!