I have access to gauges but never really knew exactly what I was looking for in terms of pressure.

Do you have the proper procedure for checking the pressure (Fan in front of car, rpms at 2000, etc.)?

High side should be 2.2 times the ambient temperature in Farenheit.

No, it'* a gas; you wouldn't be "flushing" anything useful (and at $65/pound for Freon, that would be a bit of a waste... ).

All things are possible. First of all, the compressor is actually operating, right? You can see it turning when the engine is idling? (It may cycle on and off by itself; the main point here is whether it operates at all.) You have decent airflow coming out of the dashboard vents?

Assuming Yes to the above, does the air temperature get noticeably colder occasionally while you're driving, such as after making a sharp turn (especially a left-hand turn)? This could indicate that you're low on Freon. I'm assuming you are, from what you're describing, plus it'* normal to lose the stuff over time (i.e. years) as it can permeate right through the hoses, long-term.

But given the price of Freon, if your system is otherwise in working order, go get the system pressures measured correctly and see how much you really need to add.