You sure know how to pick them! This will be a challenge.
Bad news, buddy. Just checked availability of the drain valve from Hobart and there are none available anywhere and the number has been deleted from the parts inventory system. There are 5 shaft seals available but not all in the same place, with the closest one in the Chicago office if they still have it.
The water leak that seems to be near the motor may just have been a loose screw on the mounting plate in the tank. DONT take the motor out if it is running nice and quietly. Unless you can find the gaskets leave it alone. Tighten the screws and be done with it. The seal goes in from the top very easily too.
There seems to be some water trace lines that have followed the tank contours which is somewhat normal and have dripped down to the motor area. Once you can fill and run the machine, you will see where they are coming from and work to fix them.
See if you can get a valve from one of the members here or find yourself another machine as a donor. I would plug it in and do a test run on the motor at least and see how it sounds. you wont really harm it if you run it without water for a short period of time. That way at least you know if it runs or not.
As far as the lime scale goes, if you live in a city with naturally soft water or you have a softener in the house, when you get it running, the lime will all come off in time with regular use just because the soft water will strip it away. You dont need to run any deliming solutions in the machine and even though the porcelain looks pretty good, I would not want to compromise it with any type of acid if it isnt necessary. Then you will want to check further for more leaks as the lime may have self sealed some of them.
I think you will get it all put together with the help of the members here.
Just take it slowly and get your parts lined up after you know the motor at least works!
Keep asking us questions and we will all be glad to walk you thru it.
Steve