Project: Armchair on wheels

[bigsharn]

Ok, well I'm in need of a new bike soon as my last one got nicked. I'm thinking about getting something like the Dawes Discovery 401 (48-11 gear ratio is very attractive.), but part of me wants something a little more unique...

I'm thinking of getting my own chopper built, something like a beach cruiser or maybe something a little more laid back. Currently I'm looking at getting a Schwinn Corvette Cruiser and modifying it as I go along, starting off with replacing the rear cassette with a geared hub, and maybe swapping the front crank with something with more teeth than the norm (possibly custom CnC milled), to make a cruiser that's capable of decent speed AND able to hold my weight.

So, basic questions:
1. Does anyone know how thick a piece of alu/steel will have to be to support a decent amount of force for pedalling and so that it won't bend/snap?
2. I'll be laid back a fair amount when the handlebars are raised and modified enough for me to do so...
a. What would I use to replace the handlebars? I realise you can get them premade but I've got an idea for making them out of tubular material, the only problem is making the grooves that keep them in the headset
b. Can anyone name a decent leather-like substitute to upholster the seat with? The idea is to have like a Raleigh Chopper but a bit more laid back (And if anyone has an idea for a good stuffing for the seat, that would be good too)

Probably more to come, but thanks in advance (so far)
Sharn