When I woke up my '77 after a 28 year nap (with what was probably almost a full tank of gas when it was stored) I did pretty much what geoluv outlined, except I didn't bother with the 5 or 7.
I would add to replace the fuel lines with fresh rubber now vs later. Also before you do more than test rides around the block install new tires, tubes, and rim strips. You don't need fancy tires for these bikes. You can get a set of Kenda or Shinko's for less than 100GBP.
#1 on my list would be to empty the tank, pull out a small flashlight and inspect the inside carefully for rust or gunked up old gas. If you need to clean the tank remove the petcock and take out the small filter that is inside the tank. If often stays stuck inside when you pull the petcock, but it is there. Remove it carefully and clean it with carb cleaner. Leave it out while cleaning the tank as it is easily damaged.
The oil brand isn't really that important, just make sure it is motorcycle specific oil that is suitable for bikes with wet clutches. I would personally recommend conventional vs synthetic. But in any event stay away from car oil as it includes various additives that will mess with your clutch, which shares the engine oil.
The carb's aren't bad to rebuild, but the PD style carbs on the '77 and '78 models are a bit different than the earlier carbs, so when you order a gasket set make sure you get the correct ones. You don't have to separate the carbs to clean them, but you can do a more complete job if you do. It took me 2 weekends to do the job. Take your time and do them one at a time and it should be fine. Definitely re-use your old jets. if your kits come with new ones (get gaskets only if you can) just set them aside. The sizes of the holes in the non-OEM brass are not reliable and can mess with your ability to get the bike to idle and run properly.
Take your time and be systematic.
There are some tools worth buying. Vintage Japanese bikes like this use screws with a JIS head. It looks like a Phillips style, but is actually slightly different, and the difference often leads to stripped screw heads. Spend the money on a set of JIS screw drivers, they can save significant aggravation and stripped screws. I would also pick up a valve lash tool. It's a special tool for setting tappet clearance. You can use regular feeler gauges, but the dedicated tool is not expensive and makes the job MUCH easier. They come in a couple size combo's, so make sure you get the right one for your bike (.5MM/.8MM I think).
You will likely need fork seals, they are cheap and easy to install. The Allballz upgrade is nice, but if your fork steers smoothly, not necessary. Both my prior '77 and my current '75 have the original ball bearings in them. As long as they are properly adjusted they work just fine.
