How much reverb?

It really depends. I love reverb and I use it always so I have tens of 'favourite' reverb presets. In general you'll need less for rhythm, and less for lower gain sounds. (surf aside ;)). So a long sustaining solo would have a fairly high reverb with me while a blues rhythm guitar would have none. But the other paramaters are important as well, having a low reverb with a huge tail can give nice spacy effects as well, just experiment as much as you can.

I like the way a LITTLE reverb warms up my tone so I always leave it on for rythym and tend to turn it off for leads.

I like lots of reverb, usually between 2-3 on my HRD, but for Surf music type tones (which I really like), I will crank it up to 7-8 or even higher. Big reverb also sounds great if you want to get those 60's psychedelic type tones as well.

So it depends on the music. If I'm playing Metal I will turn reverb way down (or off).

As far as "room" or "hall" these are terms to give you an idea of the depth of a reverb. Small room will sound like the echos you get in a small room, Cathedral will sound like you are playing in a huge expansive room with very deep and delayed echos. Gated will cut off suddenly at the end. Hall will sound like somebody at the end of a long hallway...

You really have to choose for yourself. I use different amounts of reverb according to the type of music I'm playing, I don't leave it at one setting all the time. I like reverb more with clean tones, and not so much with overdrive or distortions.

Hard to measure, but I don't like it up much past 3 on my Fender amp. It gets too weird for me.

crank the reverb (not the ketchup though) :roll: Make it as splashy as possible please!

No, like you've heard, it all depends what you want.