What would happen if I cast True Strike, then True Target then used my third action to strike (rolling twice) then for my hasted action Strike again, would it benefit from the True Target?
Both spell effects would try to apply to that first attack 'The next time you make an attack roll' (True Strike) and 'The first time each targetyou make an attack roll during the spell's duration' (True Target). And the Fortune trait would prevent that from stacking.
You would only get double rolls on your 1st attack, but you could just true strike -> strike ->true target -> strike to have both attacks get double rolls.