Usually the player given the simul takes White (I always did) but it's not
unknown for them to offer to play Black.
The rules about passing should be explained before the start.
I allowed 3 but some allow none.
Often read reports about a certain English GM who if you did not move
the moment hr appeared at the board then the pieces were pushed into the
centre of the board. Game over - you lose.
Don't play anything odd in the opening you will be playing right into his hands.
As Black just hope he plays 1.e4 you do OK in that opening with your classical 1...e5.
It's against 1.d4 you are having problems.
You dabbled with 1.d4 d5 2.c4 Nf6 for a while.
But lost the majority of your games v 3.cxd5.
Now you are relying on the QGA 1.d4 d2 2.c4 dxc4
But are having a torrid time with it.
Two examples of you as Black played late last year.
and Game 8702431
in both cases you get chewed up
in 10 and 16 moves.
Tactically you are OK when on the attack but defending and spotting shots
against you, you need beefing up in that department.
Your sense of danger is low.
Though OTB when you are playing just one game giving it 100% concentration
you may be different. I can only go on what I see here with your game load.
Nothing wrong with the QGA if Black plays it correctly.
Challenge, have a word with or look at the games of stephenwale User 53895
He has over 100 games on the Black side of this opening.
He often tries to hang onto the c4 pawn in the QGA and comes a cropper.
Looks like a game of yours given above.
So you learn from his mistakes rather than from your own games.
Good Luck Mate. (get castled ASAP with either colour.)
Get a picture taken of Shirov at your board then send me the pic and the game.
I'll blog it.
PS: book up on the QGA. You never know Shirov might read this post.