The minimum effective number for FoF teams would be 10, you have to balance effectiveness and cost. Bigger the squad the better, so 3 teams of 8 wouldn’t be too good. Sure the
teams are cheaper, but you have to make the 70 point minimum for the Devilfish worthwhile.
Fusion on Stealths mess up the squad. They are dedicated to tackling light infantry, once you add in a single (or 2) weapon designed for different targets at a smaller range you must bring your guys closer, which leaves them more vulnerable to return fire. Without target lock(s) on the fusion, you waste burst cannons on vehicles (after all, if you need the fusion you are shooting at AV burst cannons can’t harm), and for the melta range you basically throw away the squad. Deep striking
Sunforge (twin-linked fusion) are better, they hit more often, have a direct path to vehicles and cost around half the price straight up. Only time it would be viable is when you have no railguns, and rather take Stealths over Crisis Suits, as they would handle it much better.
Shas'el - 100pts
Cyclic Ion Blaster
Airbursting Frag Projector
HW Multi Tracker
Targeting Array
CIB good, AFP bad. You got the BS for the CIB, but the AFP wastes your commanders natural superior BS, and then you increase it to BS5. It’s only good on Shas’vres as there is no BS to waste.
XV8 Team
1x Shas'vre +Targeting Array +HW Multi Tracker +Plasma Rifle +Missile Pod - 82pts
1x Shas'ui +Multi Tracker +Plasma Rifle +Missile Pod - 62pts
If the target array is that important, at least take a team leader instead. Shas’vres are useless, apart from fluff and access to special issue weapons. Team leader is just as good, he has access to hard-wired equipment at half the price.
XV25 Stealth Team
3x Shas'ui - 90pts
I find the minimum number for Stealths if 4, that’s where they start to do stuff. For every squad of 3 or more Battlesuits take a team leader and bonding knife, there’s no need for your expensive heavy-hitters to run away like cowards. Well, not too early anyway.
11x Fire Warriors +1x Shas'ui +Devilfish - 210pts
Decoy launchers. For such little price you get soo much durability.
Hammerhead + Railgun +MultiTracker +Burst Cannons - 160pts
Decoy launchers, target lock. What ever you shoot a slug at will waste the burst cannons.