Welcome to the forums. Yes, you can use a non tap-shift transmission as long as it's 04+ for a direct swap. You have a lot of questions so I'll try and address them all but may miss a couple.
Other upgrades that should be done if you plan on putting down 300whp and above.
300m input shaft and single 7/8" chain upgrades are the main ones.
Stock axles will be fine for anything that you'll be doing unless you're trying to cut 1.6 60ft times.
With your car being a Comp-G it already comes with the 3.29 ratio which is a far as I'd go. Turbo guys prefer 2.93 ratio (or at least I do).
Valve Body and Channel Plate upgrades are what really wakes up these transmission along withe modifying the spacer plate that goes in between the two. Along with the the shift kit assumed.
A transmission can be done on the cheap for $500 and to handle 275whp
Add 300m to reach 325whp
Add 7/8" setup to reach 375whp
Valve body and channel plate upgrades are personal preference. I HIGHLY recommend them being done.
Your BF is correct. I have run a similar hydraulic oil in combination with my setup and Dave at TEP also recommend it.
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