What Size Pressure Tank?

I have a seasonal cabin that's been in the family 30 plus years. I have no idea what type of pump is in the submersible well, nor how deep, nor how old. The pressure tank in the cabin still works, but want to pull it to replace flooring. Has no where to check pressure or ad air, unless it is underneath where it can not be accessed. Currently have 30/50 pressure switch and I have 1 kitchen faucet, 1 lav faucet. 1 toilet, 1 shower, 1 water heater, and one hose bib. How big a tank would be sufficient? Would like to go horizontal if possible to save space. Thanks in advance for any & all replies.

If your existing tank is working fine, there might not be any need to replace it. And, it is likely already a bladder tank with an air valve somewhere. But if not, adding a tee to add an air valve can be done just about anywhere on the tank.

As to horizontal: I was able to do that with one of my tanks in a crowded space because of its inlet/outlet location. However, I would not want to do that with a tank like my darker one that has the inlet/outlet in the center of one end. A key facter here, however, would be a solid mount for any tank.