1) Standard loft varies by manufacturer. Most standard lofts that I have seen are 3*, Scotty's standard loft is 4*, Rife's standard loft is 1*.
2) I would stick with stainless as it will be easier to maintain than carbon steel. 303 Stainless (or is it 304? I am getting old and can remember) seems to be the metal of choice for the boutique putters.
3) Head weight varies by manufacture. Scotty swore by 340 gram heads for his 34" putters for years, but I personally find heavier head weights more desirable. 350g, 360g, heck even 400g if you can do it. Better yet, build some weight ports that you can put different length bolts into so you can adjust the weight. 
4) As has already been stated, you do not need a specific putter shaft, any shaft will do. As Rick mentioned, I would go with a .370 shaft/bore as it will be easier to do and easier to find shaft for.
Take some photos as you go along in the process so that you can go back and enjoy the stages of development later on down the road. Of course, I always intend to do that with every set I make and never remember to do it. :laugh:
Lets us know how it goes, I look forward to seeing your progress. 
I built a putter in wood shop while I was in 8th grade. I made the whole thing out of hardwood (head shaft and shaft anyway) and screwed on brass plates for the face and sole. I hand wrapped the grip with leather and was pretty satisfied with the result. Your project sound 10 time more exciting as you will be coming up with an modern putter. My 8th grade project is more of a decoration these days. Too fragile to use or put in a bag.
Crooked Cat + Crooked Driver = Crooked numbers on the card.
"Rodney has left the bag"
Ping Rapture 10.5* TFC 909 Regular
Ping G10 17* 4 Wood TFC 129 Regular
Bobby Jones H3-21*, H4-25*. Graphite Design JS-7 Stiff
Ping i10 5-PW, UW, SW, LW, Z-Z65 Stiff, WRX Custom TS Grind PW-LW .
Rife 2 Bar Black Mallet. 33" 150g TLP back weight.
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John "Bravo" Bretz 1955-2008
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