Was your AC working before you added the freon?
I once had a leak from the high line into the compressor, I changed the o-ring, vacuumed it and re-added freon and has been working for almost a year now.
There could be a leak in your system. On mine, I tried refilling it, it worked for a day, and then stopped. My friend noticed small bubbles from where the leak was.
1) The gauges on the AC cans are not that accurate, but can be used as a rough guide. AC gauge manifold is the more accurate option.
2) There may not be enough freon in your system. I say that because your compressor periodically shuts off, and the pressure is not up to range, yet. From what I observed before when re-filling freon, is that the compressor shuts off if the pressure gets too low, until enough freon goes in, for the compressor to work with.
3)There may be a leak in your system. You can use the UV leak detect stuff, some may come with freon. A lot of people are against the stop leak
That being said, if your AC works throughout the season, you should be fine.
I believe my low side pressure was around 38-40psi at around 75 degree temperature after it was filled with the AC on, and I think it took 2-12oz cans (I'm not sure if I opened a 3rd can).
I briefly looked into the 1998 Legacy Service Manual and it said to keep the pressure below 40psi, btw, I'm not sure about your Forester or WRX. I hope all this helps, and your ACs blow cold!