Congrats on getting into a mustang. They sure are fun, low cost cars that with seemingly endless modification possibilities.
Bolt-ons will only net modest gains at best.
If you want some decent power gains I'd consider a split port swap from a 99-04 3.8L v6. The improved intake/head design and will bring you up to the 99-04 3.8 hp numbers ~ 193 vs your 145.
It's a great bang for your buck mod and will allow you to work on your car and learn a lot about it. A windstar intake upgrade will net and additional 8-10hp and won't take much more effort if you're already swapping to split port.
Below is a link with the full list of what's needed to complete the swap. Seems like a lot but most of it is covered if you come across a junk yard car.
You could also look into an m90 eaton from a thunderbird supercoupe. These have been known to make some decent power but do require some supporting mods to fuel, air and drivetrain.
12 Black GT500 SVT PP l 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.