New to this world.

I recently purchased a Paxton Sn89 kit and I have a few questions. I have a 1989 Mustang Gt.
It has an upgraded impeller, how much difference does that make?
By all accounts I will see 6-8 psi, at what point do I need to worry about a bypass valve?
Do I need a BTM right away?
I got a good deal on this kit but it doesn't come with a radiator hose or intake tube. I can handle the radiator hose. I am thinking of making an intake tube out of silicone elbows and either CPVC or aluminum pipe. Which would be better? I know UPR makes a plastic one and AFM makes an aluminum one but I have read that the UPR pipe does not suffer from heat soak as bad.

7PSI and Above, But it would not hurt to put one on Anyway =)

The upgraded impeller typically provides an additional 1psi to 1.5psi. May not sound like much, but for it's cost, it's a worthwhile upgrade for an SN blower.

You won't need a by-pass valve at the boost levels you'll see from the SN blower. If/when you upgrade to a blower with higher boost capability, then you'll need a by-pass valve. But for now I wouldn't worry about it.

I don't have a lot of experience with intake tubes on SN blowers, but I can tell you that on 4th generation Corvettes ('84-'96) they didn't even USE an intake tube. The air filter was slipped right over the blower's intake volute. And even though the air filter was close to the exhaust manifold, the boost and flow numbers weren't any different when compared to those owners who fabricated their own intake tubes to try and alleviate the issue of the supercharger ingesting hot air. I don't know if the same holds for Mustang applications, but I'd imagine it can't be much different. Unless, of course, the intake tube is required in order to locate the mass air flow sensor...?

I Use the AFM Powerpipe with my SN89 and VR4 and it works great, Yeah, it costs more up front, but Think about it this way, If someday you decide to upgrade your blower to say a Vortech or Pro-Charger, you will already have the setup there. I also Run a 90MM Lightining MAF, 38LB Kenne Bell Inj, 65mm TB, SCT Eliminator Tune, 255LPH Pump, I am all set up for future upgrades, No Bypass on the SN but I did put one on the VR4 setup that I have yet to run. Spend a little more money now and you won't have to later. Actually I am thinking about selling my VR4, but not sure yet. :P Need the time to finish the setup but with working 70hrs a week, that makes it hard to do. Like Michael said, you don't need a Bypass, but like I said, it can't hurt, Or I should say, putting a Bosch style on will not do any harm, but you do NOT need to worry about it. Only when you get above 6-7PSI you will need one. BTW, just to offer you a bit of Info about what my SN89 does for me, With that setup on my 89 GT Stock baseline RWHP was 186.2, With the SN89 and all the stuff I listed above, I got it to 277.7 RWHP with Stock E7 Heads and Stock Upper and Lower Intake for a Decent 91HP Increase to the tires. this spring, i will be putting on my Ported GT40 iron Heads 3 bar and Ported Explorer upper and Lower and better headers, so it should Breath better. Max Power was made at 4800 rpm and Max Boost was 5.7PSI also Timing Advanced only 2 degrees. Just so you can get an idea what you might see out of your SN89 if you set it up right. Forget the FMU and get it tuned with better Injectors, Just my 2 cents.