My 3L UIM swap was very successful and felt like a minimum 10-15 HP/TQ gain, but I also already had the dual exhaust to support the other mods. Your results may not be as dramatic, but should still be good.
My advice is to not use 24# injectors unless you P&P the heads, add headers, and the other planned mods you have listed. The 19# units I swapped out for the 24# units were more than adequate for this engine on the stock ECU. Unless you're still running on the stock injectors (17# for non-SVT), then I would suggest not using the 24's.
If you do need to use the 24's, then get a MAF optimizer for your stock MAF. No need to go to an aftermarket MAF for your set up at this time. The thing is, you could do a dyno run, send your AF ratio specs to a chip burner, and get a custom chip for not a whole lot more. I'd just save up for the chip to do right after the intake swap if I were you. The stock ECU can handle the 24's for a short while, though it will be pig rich until you get the chip.
