Welcome to the world of Supras. They're not as picky as DSM's, but they're close
First things you should do:
Perform a Compression Test, Leakdown Test, and Block Test.
Then, change the engine oil and filter(wix, i.e. napa gold, carquest. or purolator pureOne filters are really good), transmission oil(redline MTL or the like), and differential oil.
Change the fuel filter(wix).
Just so long as you don't use Fram, really.
IF you have good compression, I would retorque the stock head bolts to about 72lb/ft and see how long that lasts.
If you do blow your headgasket, you can't simply slap on a MHG, theres a lot of prep work involved. The 7M is a picky engine when Headgaskets are concerned, so you have to be very meticulous prepping the block and head for it.
after that, and only after that, should modifications be done.
Intake, I would suggest AEM DryFlow. No oil necessary, so you can't over-oil it and screw up the AFM, they're reasonably priced, and filter great.
BOV I can only see doing if yours is leaking. If you're doing it just to say that you've got a BOV, it's not worth the money. If yours is leaking, however, I would suggest picking up a Bosch 110 (or whatever model they are now :icon_razz) One or more of our vendors sells a complete kit that includes everything you need to install it and go.
Downpipe, I would suggest, as others have, a DP or DDP from BIC (
www.bicperformance.com)
he makes some of the best parts available for these cars, and he's a member. May as well support a local guy.
Catback is purely preference. I had a crush bent 3" with an N1 can at the back. Sounded awesome. The hanger bracket broke off of the muffler, so I took it off and ran open DP. That sounded awesome too. It's all personal preference.
Exhaust cutouts are available through
www.summitracing.com
I believe the brand is Quick Time Performance, keyword search QTP comes up with them IIRC.
Oh, and always keep the oil a quart overfull. it'll be nowhere close to the crank, and it keeps the pickup a little more submerged in the oil, as the 7M's oil pump pickup is just a little too high in the pan.