Updated OP for specific players, action, etc. I don't mind this being a quick one since I have Mike and the Dr. here with me.
Big O - 5 Card PLO Hi/Low .10/.20 w/ Mand Straddle
SB Solid Player $58
Big Blind Drives Action $185
UTG Unknown Player $100
UTG + Action Junkie $371
MP1 Hero $255
MP2 Solid LAG $255
HJ Somewhat Passive $53
CO Unknown Player, but has shown aggression $181
Hero has 2/2/3/8/K. Image is a LAG, loves big hands, loves to chase but also put pressure on others. Big wins, big losses.
Straddle gets called around the table, SB raises to $3.40. Everyone but UTG calls until CO repops to $9, everyone calls.
Pot is $63.40
Flop comes 3/3/K
First 4 players check, Hero in Middle Position....Action?
SB/BB/UTG check through, I check through to the aggressive players behind me, which also check down.
Turn comes, 3/3/K/4
SB Checks, BB Bets $5, UTG+ Calls $5, Pot is now 73.40 and Hero.....
I assume the button folded at some point?
Was there a FD on the flop? If so did the turn complete any FDs? I know it doesn't matter to you since you flopped the FH, but FDs are probably important to some of your opponents.
So here's why you need to bet the flop. Chances are there are at least one and maybe both A2 combos in the field - and they both hate this flop. One of the aggressors (probably the CO) might even have AA2. You can also extract value from from a player holding the other 3... with 6 opponents there's a good chance someone has it. This is how you leverage your table image to get calls from weaker hands whereas a nut-peddler has difficulty getting paid off from observant opponents.
You also don't want to give a free card since unless the turn is the case 3 or a King, you're about to go from holding the 2nd nut to the 3rd nut for high and now there's a low draw possible too. Your 8-2 doesn't even qualify as an 'emergency low' against this many opponents.
So from the CO's perspective, he's not going to c-bet into 6 opponents with nothing but an overpair and a backdoor low draw on a paired board.
So on the turn, you have the 3rd nuts for high and there's a wheel draw, which probably excites several opponents since no one bet the flop.
The $5 bet from the BB is comically small. I suspect they're holding bare trips and are hoping to get the river card cheaply. In fact, it kind of feels like everyone is trying to get to showdown as economically as possible.
I'd probably bet full pot here (~80ish). You want to make the low draws pay as much as possible. It seems unlikely someone would have slowplayed KK* unless checking to the aggressor is the standard line for everyone like it was for you on the flop. 44 will probably call but not raise. You might get jammed on with A2 especially if they have counterfeit protection and/or a FD to go with it. A256x definitely isn't going anywhere.
I think if you get jammed on you're calling if it's the SB or the CO. If one of the other players who've been passive to this point sets you in you probably should consider folding.
There's also a case to be made for calling the $5 hoping to peel the river and get to showdown as cheaply as possible. There's a good chance the low draw will come in for someone... so if you've resigned yourself to playing for 1/2 the pot you might as well take a passive line.
*I think the only case for slowplaying top FH on this flop is if you have a2 with it... presenting the opportunity to scoop a much larger pot. A2KKx is an oddly specific combo to be holding though.
