Reddit mentions of Clymer Honda 100-350cc Manual M315

A really good source for info : www.dotheton.com
Make an account on that forum and when you're done with that go to the forum and find the "projects" section and look for the subsection "cafe racers" All of those threads in there are packed with information and each thread has the bike's year and model in the title.

For more focused knowledge use the search function and make it so it only searches "projects - cafe racers" and search for Honda CB100 and the CB125 (it's literally the same bike just the displacement of the cyl is different). There you will find threads about your bike and they will contain many photos of the build process to help you.

Parts for CB100/CB125s : search ebay for brake cables, clutch cables, and throttle cables. That bike's model is super popular in Thailand and they still make new ones I think so all those parts are still available but ship time is long. Buy these now before you have to in the future and wait 1 month for shipping.

I tried getting a replacement CB125s wiring loom from ebay as well but once I got it and looked at the wiring diagram it turned out to be a CB100 wiring loom which is slightly different when it comes to the alternator connections and rectifier/regulator. That's good news for you though it means you can easily find CB100 totally brand new wiring looms. Replacing yours would be a really good idea unless you've seen your wiring and it looks mint. This will help you avoid any strange intermittent electrical issues.

I converted my CB125s to 12v but I have an '81 and it uses a Pulse-CDI ignition so it's not the same as your CB100. It will be a similar process and shouldn't be too difficult. Dotheton.com might have some threads on that.

Cleaning and rebuilding the stock carb is ideal but if it's cracked or un-cleanable replacing it with a Mikuni-clone ebay carb will work. I did it and it started up instantly and has been running strong since I switched.

Hard to find knowledge RE: single cyl. 100-125 thumpers from Honda : they don't mind K&N airflow or Uni-filters and can use them fine since the carb is slide and not vacuum. However, these bikes do not like shortened exhaust manifolds/mufflers. These bikes prefer longer exhaust manifolds with a longer muffler for backpressure so don't shorten it any shorter than it was stock.

Lastly : if you intend on changing the clutch plates it's not that hard at all but you will need a specific Honda OEM socket to remove a bolt on the clutch basket. They sell it for like 50 bucks the bastards. Many people make their own. It looks like this : https://www.50stunt.com/v/vspfiles/photos/MMEG-TBW0307-2.gif

Definitely make your own don't be like me and pay half a hundred for that.

Good luck!

http://www.hondatwins.net/forums/62-engine-discussion/19731-clutch-hub-nut-socket-how-make.html
example of someone making their own clutch tool. I think there are many types though 20mm, 24mm etc.

You will 100% absolutely want to purchase a clymer manual for your bike : https://www.amazon.com/Clymer-Honda-100-350cc-Manual-M315/dp/B000GTVNNS