I don't have recent experience with indexed derailleur shifters, but I think any of the Shimano bar ends will work for you in the indexed setting. If you plan on friction, you can use any bar end shifter (Suntour, Camapagnolo, Shimano). An old Barcon is tough to beat.

Newbaum's cloth tape comes in eggplant. Other colors could be made purple with the right shellac and number of coats.

As for fenders, I like aluminum or stainless if you're going to be rough on them. That's mostly because I don't like the way plastic fenders look.

I'm assuming your bike uses 559 wheels and not 622.

I have no experience with tires on snowy roads, but I'm also looking to build up a vintage MTB with fenders and studded tires if/when I find one 23" or bigger.