I say start out simple, then add stuff if you like it. Try your load on a ride around town, change things if it doesn't work.
Consider a down quilt for a smaller, cheaper alternative to a new bag. The one I bought for a bike tour, the Revelation 30 by enLightened Equipment, is perhaps the best piece of outdoor gear I've ever acquired. I just use a Z-rest for a cheap, durable pad, and try to camp on grass for a softer bed. I carry a single-wall silnylon tent made by Tarptent, also relatively inexpensive and easy to pack small. Look at Arkel Dry-Lite bags.
I'll also throw in an unsolicited story about my first tour in 1975, on a Schwinn Continental with one of those old steel book racks on the back. I loaded the sleeping bag and tent on rack, rolled extra clothes in the sleeping bag, tied an old gym duffel between the brake hoods for food, and took off from Chicago on a 1000 mile tour around Lake Michigan. It worked, and I don't think I've ever packed the same for any subsequent trip. Keep learning.