I'm surprised the usual Wurlitzer crowd haven't chipped in yet!
The 4035 is an OK organ, dates from 1970, but is pretty much basic electronics. As soon as I saw the model number I thought "The cassette player won't be working!" Sure enough, you post says that it isn't, but they didn't work that well when they were new.
It makes a good old fashioned electronic organ sound, biased towards theatre organ voicing, so don't expect the trumpet, for example,to sound like a real one! It has a built in drum unit called 'Swingin Rhythm' and has the 'Spectratone' rotating speaker system. This, being mechanical, might need a bit of maintenance. Any faults are usually basic and hopefully not too difficult to fix.
If it's free, go for it and enjoy learning to play. Once you start, the organ bug often bites and you'll trade up to something bigger and better. Thankfully, with the organ market as depressed as it is, that process will be inexpensive (unless you want a tonewheel Hammond or something reasonably new). Let us know how you get on, we'll be here and happy to answer any questions and help get you started.
The World needs more organists!!!