So, let's assume TB is decided upon.
Character movement might be regulated through Action Points, like Fallout and Wasteland 2, but this is not set in stone.
If turns are strictly sequential, then each character must complete his turn before you can move on to the next. Alternatively, turns might be more fluid, allowing you to move each member of your party in any order, even jumping back and forth between them, until they are out of actions or you choose to end the turn (e.g. you could move every party member into position first, then have them each attack in turn before ending the round).
In the first, sequential method, the turn order of party members and enemies would be mixed, based on initiative order. In the second, fluid method, initiative would determine which side (party or enemy) acted first, then all members of that side would take their turns together.
What do you think of all this? Would you rather be for a strictly sequential system, or for a more fluid one? I think I'd rather be for the latter.