I find it hard to stay on track with my seams without having some sort of marking to follow on my FW. I have seen people mentioning to use painter's tape, but is it a good with an antique machine? If it is a bad idea, what should I mark it with?

I use about 3 or 4 layers of the blue painters tape. No damage....does great.

I also read where others use a stack of post it notes

How about a 1/4" foot for it? I love mine and piece with it all the time. They do sell a needle plate with seam markings, but it's about $50.

I use a product called mole skin. You'll find it at any drug store even walmart has it .It's in the pharmacy section aroung shoe inserts. Works great for me , I have it on all my machines but I also use a 1/4 foot ln my machines.

Just don't use regular old masking tape. The first FW that I got was a real mess and I managed to get her cleaned up pretty well except for a piece of masking tape that had either baked in an attic or deteriorated somehow and welded to the machine and no amount of work got it off, there is still a faint image of it there. That's all right, she purrs along and doesn't even know she has acne.

just remove it at end of day i dont leave it on overnight

I have used a pad of sticky notes from $ tree and split in half and then cut the half in half for a guide

I measure 1/4" from the needle & place a refrigerator magnet with the straight edge toward the needle. If you need to, you can always reposition it but I've only had to do that when I wanted a different seam width.

Dritz makes a magnetic seam guide that attaches to your machine throat plate. Joann's sells it for 4.99. Holds tight, works great but don't use it on a computerized machine.