Here is what I would do assuming the video shows the current condition of the bike.
First, get a good cleaner. My favorite is S100, but you may not be able to get it where you are. A lot of people like a heavy duty cleaner like Simple Green. Get some cheap paint brushes and several sponges. Spend a couple hours cleaning every spot on the bike. Do one spot at a time working the cleaner with the brushes and sponges and then rinsing. This will make a good starting point for working on the bike. A clean bike is always easier to work on.
Then, if you don't feel able to do a complete disassembly of the bike, go at it section by section. Remove whatever you can, and while it is off the bike do another careful cleaning and inspection. Make any needed repairs and get the parts ready to put back on the bike. Clean all the electrical connections with Deoxit D5. This stuff has been used on many K bikes to clean up and protect all the electrical connectors. It's one of the most important chemicals to have in your shop.
While everything is off, clean up the rust on the frame with sandpaper. Wipe down with paper towels and rubbing alcohol. There is no need to remove all the rust, just get as much as you can. Then spray the area with a rust converting primer. This converts the rust to an inert compound that you can the paint. It's easy to mask off the surrounding parts with plastic bags and sheets of newspaper.
With all the parts clean, repaired and painted where necessary you can start to put things back together. With everything clean, working will be more pleasant, take your time and put everything back with anti seize and the proper washers and nuts. If you can get one, use a torque wrench.
Don't worry if you can't remember how something goes together, you already know you have support here to help you get things right.
I realize that the area under the tank looks intimidating. If you take your time, you can move things around enough to be able to clean up the rust and get it painted without making a mess of the wiring and plumbing. Just be methodical and take your time and you will be done before you know it. There are threads here where others document their restorations. You will find lots of tips and inspiration by spending some time reading them. If you can take the time and haven't done it already it will be very worthwhile to spend a couple evenings scanning these threads before you dive into your bike.