Spending more of your budget on lens to compliment the cheaper rp would be a good call. If you get the right lenses it’ll def last you a long time. A body less so.
Just think twice about investing in full frame system. Everything is a lot more expensive and heavy for benefits you might not see depending on what type of photography you’re shooting.
I’m not familiar with the eos ix. If it’s a different gauge film it would be a matter of sourcing it and then finding out if your local photo shop processes it or learn to develop it yourself. A-1 is still pretty popular these days. I have an ae1 I use time to time. FD lenses are still being used in mirrorless world so can be easy to find in second hand market.
Enjoy! Film photography isn’t just for the hipsters. It’s hella fun and the purest form of the craft itself. Just expensive…