Well a 12 x 18 inch piece of 4 oz cloth with burlier fibers weighs maybe 0.8 ounces (includes bottom in 18 in length as well as sides). The same piece of 1.4 oz silnylon weighs 0.25 ounces. So to save a half ounce I don't think its worth the loss of abrasion resistance at a likely higher wear area. When I make a rear pair I'll use oxford again, and not just because I have material on hand. Ounce you sew the mounting hardware making patches and repairs are harder so making it more robust up front makes sense to me. But if these are a one shot item or the goal is the lightest possible, silnylon with designed in reinforcements might work ok.
In terms of assembly, having a sturdy stiffer fabric to sew the silnylon too actually makes sewing easier. The silnylon stil wants to slip around, but you only have to chase one piece of fabric instead of two.
I use an 11' by 11' 1.4 ounce silnylon catenary ridge tarp that weighs 17 ounces instead of a tent. It covers me and 2 bikes and my buddy slept in a small tent he carried. Bike touring I never camp above treeline so poles aren't needed, I just guy it between trees, or whatever is around. A mosquito headnet is useful even with a tent. The other big weight save is a down quilt or top bag.
Being able to plan water stops allows one to minimize water weight. Alcohol stoves are great for bike tours as fuel is available in lots of places, but usually more than you need unless you have a big group. But make sure you test the stove for pot stability and windscreens are absolutely necessary with alcohol. I find myself bringing a canister stove just to minimize fiddle factor and wow my cycling friends with a titanium stove. Well, I'm pretty sure there's titanium in there somewhere, and way more impressive than a titanium tent stake.
I haven't needed a puffy layer when cycle touring in mountains in summer. A base layer, LS jersey and wind layer with gloves, booties, and ear covering allows riding down to freezing and stops usually involve a warm shop for hot coffee or grease supplemantation. I use a very breathable windshirt (cycle cut) for all but downpours and a Rainshileld O2 propore 'disposable' rain jacket for riding in heavy rain. They work well for cycling since the only abrasion to worry about is a crash, which will mess up any jacket, and are more breathable than just about anything else waterproof. Very fashionable in a macho way too; just tell the fashionistas you work for the CIA and it wards off terrorist scare weapons and second hand smoke. I always keep one on hand when yellow rain is in the forecast.
I only carry windpants and leg warmers for legs. Rainpants for cycling have never been comfortable. Athletic windpants aren't the best for cycling (wind flap) but double as town wear.
I've made 1.4 oz silnylon rain booties and rain mitts; they add a lot of comfort for very little weight. Usualy I try to wait out storms but sometimes early afternoon mountain squalls sneak over a ridge on you.
I carry minimal tools: allen wrenches, tire irons, a kevlar replacement spoke and spoke wrench, patchkits, spare tubes, one brake cable, one derailleur cable, a small squirt bottle of chain tool, and a mini crescent wrench.
One thing about touring, if you leave something behind it's always possible to buy it somewhere. So one can err on the side of taking too little with less consequence than on a backpack trip. Also weight is carried on the bike, so balancing the load has the most benefit for handling and is probably more important than going as light as posible. Weight only really takes its toll on long mountain climbs.