I'm willing to bet if you asked around here some folks could probably find a spare Ableton Lite License kicking around if your buddy doesn't have one. They used to give them away in cereal boxes practically. Heck I probably have one stuffed in a box someplace.
I am sure it'd be dope to sequence an old Atari or Amiga PC... but learning how to set it all up is the problem. I used all that stuff back in the day, and personally don't want the headaches of too much old gear in my house. The oldest pieces I have are some old Akai samplers (S950/S1000) that I've been lovingly repairing and keeping maintained. I really like the sound, but there is a lot to be said for software samplers these days, I'll continue to argue that the software does not sound the same as the hardware, but for 99% of the people it doesn't matter because they couldn't tell. Hell, I probably couldn't tell either, I just like the interface and workflow of using buttons and knobs over clicking a mouse. It just totally depends on what experience you want to get out of it really.
To get to jamming... oof... there are a ton of ways to get there, nearly infinite with software. An also insane amount with hardware. I just deleted a ton of thoughts that were really all over the place, and got way too outside the MPC for the time being.
If you want to jam on the MPC, you really just need to learn a few things.
* How to chop... this is honestly the first step, and if you cannot get into this on the MPC, folks here can give a ton of other suggestions
* How to setup programs... if you want to perform live, you'll want to be super consistent here... kicks on the same pad, that sort of things... google finger drumming
* How to record tracks... while it seems super convenient to record everything in the program onto one track... it's generally a bad habit... because of the next step
* How to track mute... if you're organizing in multiple tracks, kick/snare/hats/bass/melody... it is trivial to track mute four or more sections and perform a song
* How to name things... this will save your sanity as well... get good at it... and get fast
* How to sequence... not necessary out of the gate, but will absolutely keep your flow and allow you to perform alongside fuller tracks in a predictable way
* How to save... sounds dumb... but save often... to different folders... you absolutely will record track mutes or other events... and being able to restore instead of having to spend several days figuring out how to erase the events you don't want and keep the ones you do is well worth your sanity
Anyways... you can seriously do tons within the MPC without needing other gear. If you can get the basics down you'll be in a better place to know where you want to add flash and flourish without having to lay down serious cash.
If you want to spend though, consider eBay, Reverb, and the like... there are great second hand markets and some of them will save you serious cash. It'll help you move gear you don't want any more, while also keeping the next gear acquisition moving forward without breaking the bank.
Edit:
A couple of examples of jamming out for #Jamuary with a stupid Pocket Operator 33... and created something that I wouldn't play live... but for something as non complicated as this you can do a lot. The MPC 1k can pull off *way* more.