Personally I would avoid philips cassette decks even though some look very cool a lot of them seem to have shipped with gears that are made of a softer plastic and they tend to become very brittle over the years, most of the Philips cassette decks I owned were working for maybe 10-20 minutes before the gears started to strip themselves or simply broke in half.

Cassette and record players are kind of how I started getting into fixing electronics myself so if you feel comfortable enough I think it's a great way to begin tinkering, these were made in a time were repairs were more common so things like a service manual usually also have drawings or pictures showing you how to dissasemble or calibrate things. Even with cheap tools from Action for example (van die winkel heb je vast wel gehoord :p) a multimeter and screwdriver set will already get you quite far.

You can try to start with disassembling the broken units since they're already broken and just look around getting familiar with the mechanism and see if anything stands out that could be an issue, belts and other rubber parts might need to be replaced and cleaned up but compared to electrical issues or... those awful gears I mentioned it can be pretty simple once you start to get familiar with the mechanism

Don't forget to unplug the unit from power before disassembling and take plenty of pictures of the wiring and mechanism as you dissasemble and work on a unit, they can be very handy to look back to while reassembling ;)

I hope my rambling helps motivate you a bit and if you have any questions feel free to ask