Beginner floundering with wood finish

Hi everyone. This is my first post. I'm not much of a home handyman but I recently bought some really good 50s armchairs from a garage sale. They were in bad shape (I think cats all over them) but otherwise pretty solid and obviously well designed. They're not hugely valuable but I like them a lot and now that I've stripped them back they look terrific, especially with the fabric I chose. A few questions for anyone with the time:

1) What should I paint them with? They're a blonde wood, I think oak (seem too heavy for pine) so I want something relatively clear. I'm not a fan of dark stains or overly "grainy" finishes - and they don't suit this era of furniture. I have some Cobathane oil-based polyurethane for floors, but having just seen that the intro to this forum specifically says "don't coat your furniture in polyurethane" I guess that's out. Any suggestions?

2) I have sanded them down to a P240 grade of sandpaper. Should I go any finer? Is it necessary if I'm leaving the surface more or less "as is".

3) One arm has a hairline crack. Should I do anything to it before I paint it, just to make it more stable and stop it spreading?

Any help any one could give would be most appreciated. Thanks all.

Welcome to the forums

I am sure someone more qualified than me will come along to answer your questions, but FWIW I would say:
3. You need to work out whether the crack is a major problem or just superficial - Wiggle things around with a deal of force and see if you hear anything that you don't like the sound of - if you do then you willneed to think of a pre-fix (usually means workingout how to remove the piece that is causing the problem and replace it with another piece in a way that will be relatively unobtrusive and also stronger than the thing is in its current form. In terms of force - think of a 10 year old boy jumping on the chair - it has to be able to stand that degree of punishment!

1. People get a bit sniffy with polyurethane varnishes. Poly is just the latest version of varnish and really can be very good for work that is going to take a bit of a beating. It does get a bad name deservedly when it is layered on so that it looks like plastic, but thin coats (wipe on rather than brush if you thin it out a bit) , rubbing down between and plenty of time between coats will give a good finish that will last and not look like it is encapsulating the wood. If you don't need the finish to be hardwearing, you could use Danish Oil (a blend of oil - tung or linseed- and varnish that you wipe on). It takes longer to dry and isn't as hardwearing, but looks more 'natural'.

2. once you get to 240 grit, I reckon it's what you feel like - I would probably go to 400 or even 600, but that's just me. If it feels smooth and you aren't too fussed, then leave it at 240. But if think it could be better and you want it to be better, then go to 320. If you still aren't satisfied, go to 400 and keep going until you say 'enuf'.

For retro furniture go with an oil- something along the lines of danish/tung- that'll keep it as light as possible.

If you are finishing with oil, you can wax with a fine abrasive pad and that will smooth things out to your liking while adding some protection.

Bit hard to give advice on your hairline without some photos- is the crack on a joint? does the hairline have any access to inject adhesive? how much flex is there?

Thanks a lot fellas. I think I'll go a little finer on the sanding and might try an oil. These chairs won't have a lot of hard wear and I am after an authentic 50s/60s look. The cracks I think won't be a problem. They're not wide enough to get anything into, they're literally hairline and I can't see any movement in them.

I might try a before and after pic when I'm done.
thanks again