For a Spring compressor, check at Autozone. They have a lot of tools that they loan out free. You have to charge them to your dredit card then they tear up the slip when you bring it back. I agree the plastic pieces are the valve seals. If you bought a Valve job gasket set you may have gotten new ones in it. If not, they don't cost a lot.

Putting new lifters on an old cam may certainly cause the cam to wear. If you have the funds, now would be a good time to change it. Changing the cam would be a lot more work than you had planned to do for sure. If not, then putting new lifters in would not cause the world to end. They will last for a while and since you probably don't plan to drive this car a lot or rely on it as your daily driver it's an acceptable alternative.

Now given that you found the bent valves, the next concern is did it damage any connecting rods, bearings or pistons? Turning the engine over by hand and watching the suspect pistons would reveal any obvious problems. But if the damage was slight you would need some precise method of measuring the pistons travel. Pulling the pan and looking at the bearings would also be a good check. The alternative here is putting it all back together with the planned/necessary repairs and hoping for the best.

I have seen a number of cars run for a long long time with flaws that ideally should have been fixed but weren't because of budget or time limitations. They were not perfect, but they ran when you turned the key. Do what you can afford and have fun with it and keep learning as you go

Pat