The player holding the 1/5 card with the star symbol starts every round. The star only marks who goes first; their first play can be any legal set from hand.
Yes, you may reorder your hand at any time. What you may not do is turn a card over, except through rotation actions or when taking cards from the table.
No, not in a 3+ player game: the set you played is discarded at the start of your next turn, before you act. In a 2-player game you have two play areas and may hold one set in each.
Nothing special happens. Each set in front of a player is discarded when play returns to them, so rotating never blocks anyone, and the table simply empties. The rulebook has no separate rule for it.
No. Sets are discarded when play returns to their owner, so the table always opens up and some play (such as a set of a size not on the table) stays available.
No. Only one set of any size can be on the table. A new set of a size already present must have a higher value; the lower-valued set returns to its owner's hand, rotated. A same-size play that is not higher is illegal.
Only if the enlarged set would match the size of another set on the table. Then it must be higher in value, and the lower set returns to its owner. If no set of that size exists, the play is legal as long as the card matches the set's value.
No. Action B targets only a set in front of an opponent, and your own set is discarded at the start of your turn anyway. In a 2-player game, see the 2-player entries.
Yes. Any set can conflict with any same-size set on the table, including your own in the other play area. If a new set beats your other one, that one comes back to your hand, rotated.
Probably not. Replies treat playing a set as one action, so if your new set beats your own set in the other area, that set returns to your hand and you have not gone out. The 2-player rule says you win when you have "played the last card(s)", and one player reads that as an immediate win, so this is not settled.
Treat it as four seats: each player takes two consecutive turns, one for Play Area 1 and one for Play Area 2, discarding that area's set first. The starting player only takes a single turn using Play Area 2 in the first round turn.
Most likely no: both actions say a set "in front of an opponent", and replies read that as opponent-only. Reports about the Board Game Arena implementation conflict, so this is not settled.