Context
I am developing house rules to use Solar system for hardcore dungeoncrawling. I've thus far run one session of the game and combat represented some problems.
Rules-wise
The characters can act independently, in which case their actions are either parallel or opposing, as normal. I might make a ruling that only defensive actions can defend against several opponents, supposing the character does not have suitable equipment (large shield or serious armour, say) to credibly fight against several opponents.
The characters can form a team (if their intentions agree), in which case they create a support chain, deal damage as one character and can divide damage among them as they see fit. This creates ridiculously long support chains, as one player opined, and hardly fits with the description of the brawling-skill (fighting in rage, fairly uncoordinated and undisciplined). Further, in fiction the characters do not always support each other.
My inclination is to go with independent actions and have some crunch that makes building a team possible. Are there any problems with this approach, in particular when it comes to speed of play or keeping track of what everyone is doing? If yes, how to deal with them?
Free and clear
In the free and clear stage players state what their characters are doing and can change their actions freely in response to declarations made by others.
In play everyone started reacting to whoever stated their actions first. Does this create any problems and should I go as far as to use some sort of initiative-like mechanic for declaring actions or even resolving them?
Sometimes I may want to keep the actions of an opponent secret; suppose the opponent is invisible, for example. I do not want to place the players in position of having to avoid using out-of-game knowledge, as forcing that on the players in this sort of game would amount to bad design. One option would be to not tell the players what the invisible for is about to do, but this breaks the free and clear stage.
If I break the free and clear stage in this way, then I could also break it in other cases: Have those who do not what is happening declare their actions first, and so on, with the most aware declaring them last. Would this be workable in play, or should I relegate it to specific crunch?