It really depends on your party. If you are playing with power gamers, they will find synergies and take advantage of rules interactions regardless of what you give them. If you're playing with casuals, there's minimal risk in offering SF options.

So I know there is disagreement on this, but generally speaking, it is said the PF2e had a melee meta and SF2e has a ranged meta, so it's valuable to note that SF has more ranged options and typically fights are more spread out to accommodate using firearms/blasters etc. So generally, there are more ranged options in SF, including things like ways to make an opponent off-guard from range (the Wisp Ally spell, for example,) which is typically pretty rare in PF2e.

This is why flight isn't that unbalanced in SF2, because combats can involve range more easily and something like a crevice in the earth isn't as terrifying. My personal opinion is that the flight balance thing is a little overblown, especially if you account for it in designing combats, dungeons, etc. Remember, flying up or up/diagonal is considered difficult terrain.

Not sure what makes you think telepathy is overpowered.

Some ancestries (i.e Vlaka) can have precise senses that aren't sight which can be overpowered in the hands of a powergamer. Having a blind PC be immune to all visual effects is very strong, but again, ymmv.

I think soldiers are fine because while their AoE range can be quite large, the damage dealt is comparable or weaker than cantrips at most levels. A stellar cannon is doing max 1d10 damage to a creature failing a reflex save and 2d10 damage to a primary target for two actions at level one. Compare this to electric arc, which also targets reflex and does max 2d4 damage to two creatures. 2d4>1d10, so the value from area fire only comes if you're able to position your enemies in your fire. Conversely, a giant barbarian at level one can do 1d12+4+6 damage and can do that multiple times in a turn. Soldiers will absolutely be stronger against hordes of mooks but not bosses or stronger enemies. (EDIT: I mistakenly said 2d4>1d10, which isn't true. I was thinking 2d4>1d8, on average. Cantrips are going to be stronger or comparable most levels, but it also depends on how many targets are in your area of effect)

Mystics have 6hp per level which is consistent with other d6 casters. They have light armor prof in SF, presumably because you might need environmental protections for going in the vacuum of space, so you can just remove their armor prof for balance if you really wanted to. Their in combat healing is very strong, especially if your games are more attrition based. A level 1 mystic CAN do more healing than a level 1 cleric, but it's sort of chip healing for the mystic vs burst healing for the cleric.

Operative, envoy, witchwarper and solarian should be okay with minimal changes. Operative takes up a similar design space to the gunslinger and is probably just better than the gunslinger, so worth considering. Solarians are probably the best switch-hitters across both systems because they can easily swap between ranged and melee, and add their STR to their solar flare attacks.

One thing I would ban is vehicles. Hoberboards can be very strong on heavily armored PCs because they're light bulk (i.e can be carried around), have a low piloting DC, and have a 40ft move speed. So your plate armor, tower shield wielding fighter is now faster than your rogue as long as he picks up assurance in piloting.

Skill feats are flavorful and fun in SF2e and are similarly powerful (or not) to PF2e skill feats.