Let's take these one by one:
FE: against hands that we already beat yes
This depends alot on the ranges of the players involved. I wasn't commenting specifically on this hand, and no read is provided for EP, just saying that this is one of the ways you can justify 3betting here.
initiative: is an over-rated concept that has nothing to do with equities and ranges. Taking the initiative gives us a stronger range and we have near the bottom of it now whereas if we flat we have near the top of our range.
This depends alot on your ranges for 3betting. If TT is the bottom of our 3betting range, then yeah, you probably want to reserve this for plays against middle and late position openers. TT is not at the bottom of my 3betting range.
I primarily play 6max rather than FR, so your statement about initiative being overrated may be accurate (though I doubt it) - but it isn't accurate when applied to 6max. Having position and having the flop probably check around to us (since most players will not donk bet into a 3bettor), and (usually) being allowed the decision whether and how much to bet based on board texture, and to be able to rep a variety of hands, isn't overrated imo.
position: all the more reason not to turn our hand into a bluff and let him re-raise us with hands that beat us and fold hands we beat
If EP 4bets and is really tight, yeah, we're going to have to fold. If EP is very tight and very agg, this isn't a great spot to 3bet. If EP is tight and passive, I love 3betting here.
Again, I was talking in general terms about justifying a 3bet, not applying it to this specific hand.
EP opener may feel squeezed: no idea what that means or how it pertains to the hand, can you expand on that?
Mostly used from the blinds. Someone opens, gets called in one or more spots, from the blinds you 3bet w a pretty wide range. Original opener has a problem - he doesn't know whether the guys who flatted behind will raise if he calls, so unless he's sitting on a hand he's comfortable getting it in with, he will frequently fold. Of course, the guys who flatted behind generally don't have monsters themselves and are playing speculative/implied odds hands to begin with, so they frequently have to fold too. A lot of leveling can go on here depending on the level of thinking of the players.
This is part of the FE thing.
isolate: yes we isolate a player who will call with a much stronger range, congratulations
You really want to play TT multiway? I'd rather play TT HU in position than multiway. And when you say "stronger range", you need to take into account both our ranges - how strong does he perceive our range to be, is he only continuing w QQ+? How about AJ+? If he knows that I 3bet 10% of the time, he's not going to put me on KK+, AK - so he shouldn't be calling or 4betting only when he's beating that range.
Again, I play 6max where weaker hand ranges are more commonly played from EP, and where 3betting stats tend to be higher.
If when you call you're setmining you're doing something wrong. You have the best hand often and a very good hand to play multiway in position, why would you turn it into a bluff? I'm assuming if he comes over the top we're folding right?
It's not a bluff. I'm not putting him specifically on a range of KK+,AK. If he 4bets I'll put him on that range, I don't think we can continue.
However, 4bets are relatively rare, unless there's a history between the players (in other words, 4bets tend to be say QQ+, AK). A lot of people will call 3bets oop w ranges that we are not far behind (and in some cases w ranges that we're ahead of w TT). Playing bloated pots in position with players who play poorly in 3bet pots is good.
Note that here there's no 4bet here, both players call, creating this exact situation. The donk bet from EP is obviously a bad sign, repping an AK or better type hand, but that's a matter of the cards that hit the flop.
I actually didn't realize the original poster said in the edit that he mixes it up here and he'd rather talk about postflop. Postflop imo is a pretty easy fold. But preflop is just a huge leak unless you have a specific read that he does not fold when we re-raise ever. In that case sure re-raise but then don't talk about fold equity, because the only reason to re-raise preflop here is if we think we have none.
There are very good things that can happen in position postflop in 3bet pots, I wouldn't dismiss that so easily.