Let me see if I can answer a few of your questions
1. Can I install just the PURE turbo upgrade on a 100% stock M235i ?
YES
2. Whats included with the upgrade ? Turbo, manifold, etx ?
Stage1 will just be the core (also cheaper on labor/install), stage2 includes turbo + manifold as the manifold required machining to fit the larger turbine wheel
3. If it can be installed on 100% stock M235i, will it be restricted substantially in power if no exhaust, downpipe, etx are used ?
If you want to get more than stock power out of your car, even on stock turbo consider a high flow sportcat or downpipe. This will remove a big restriction of airflow. While not needed it is recommend if you run higher than stock boost levels. A catback exhaust is not needed, the restriction is at the stock catalyst.
4. I want the added power, but dont want my car to sound like full blown race setup.( I do love the full race sound, but dont want the drone / louder exhaust for daily driver).
Just get a 200 cell sportcat. Your car will sound a bit louder but it will not cause drone. FYI I run a sportcat + stock catback on my F20 M135i. Its a bit louder than stock but no drone. Eg when I ran catback + sportcat I had some drone at 2k rpm on the highway.
5. Can the upgrade run safely/added power on pump gas(93 octane)?
I have found Pure Stage2 to run very well at 17 psi till 7k rpm producing +-450whp on 93 octane only on my car. I actually recommend you get stage2 turbo. If you plan on running 93 octane only, no meth this is the way to go.
6. How much is the upgrade ?
From the website: 2500$ + 775$ core charge (you get this back if you ship your stock turbo back to them after install) + shipping.
7. How much is install cost / uninstall cost ?
You should count on 6 to 10 hours labor time depending how fast your installer is. Add +- 100/200$ for gaskets etc if you want to do a clean install
8. Is the upgraded turbo reliable ?
I ran pure Stage1 for 1 year and +-18000 miles on my car without issues. The turbo is still in good shape. There is no reason to believe that they are not reliable. However since stage2 is only out since March people haven't run many miles on them yet. Eg. mine now has 3k miles on it. No issues whatsoever. The car is my daily and I run 15-17 psi with 20+ psi every now and then
9. If I dont plan on FBO & turbo upgrade, will power output be soo minimal that using piggyback easier & cheaper for same output ?
A JB4 on map1 and 93 octane only will get you maybe to 360whp. You want a JB4 to run with the stage2 turbo anyways. As well as replace your stock chargepipe with ER Chargepipe even when running higher boost on stock turbo as they are known to break. Again a sportcat/decat + intercooler are nice to have when increasing power on your car even with stock turbo. However as you can run Pure Stage2 17 psi till redline on just 93 I think it's a big upgrade.
10. Does the upgrade need better flowing fuel pump / injectors ?
As previously said you can do 17 psi till 7k rpm on just 93 with stock fuel system. That is 450whp. Want more? Add a meth kit and you will be able to run 20-22 psi and 500+ whp.
11. Is the power band output sustained across entire rpm range , or just peak rpm etc ?
You will get a lot more power in the whole rev range. Once you pass 4k rpm it becomes a total beast 
Really it changes your car totally with a very nasty top-end pull (4k-7k is insane)
12. Are they any needed electronics for upgrade ?
I run my stage2 with just a JB4 for tuning. BMS Support has been great to make a suitable firmware that works with this turbo
13. How much more fuel is consumed, if any ? Mpg upgrade avg ?
When just cruising around you wont have more fuel consumption. Of course if you use the added power a lot you will see more fuel to be used. Because more boost = more air and more fuel = more power. Since you dont drive WOT more than 5% of the time I wouldnt worry about it. It's negligable.
14. Warranty on turbo / manifold ?
Taken from their website: Warranty: All of our turbos carry a one year, unlimited mileage warranty and have been built with the highest quality parts.
My personal recommendation if your car is still stock and want more power and have a few $ left is do the following mods:
- ER Chargepipe (needed even if you tune stock turbo) for reliability purpose
- High Flow 200 cell Sportcat: More expensive than a decat but no smell and better for the environment. I wouldn't spend money on a catback as this may add drone and doesn't add any performance
- JB4 piggy for tuning the car and upping the boost
Next if budget permits:
- Pure Stage 2 turbo: Can get you 450whp on 93 octane only.
- Upgraded Intercooler: You can add this afterwards but I would do it together with the stage 2 turbo as you will be running higher boost which means more heat and you will heat soak faster. As long as you are aware of that you are good
And if you don't mind:
- Add a BMS meth kit that works nicely with the JB4. Combined with Pure Stage 2 turbo you will be going over 500whp for the ultimate N55
Hope this is useful to you and everybody else. If any other questions I will see if I can answer them.
Greetz,
Peter
Peter you rock man!
