Taylor makes a good temp gauge...they have a remote one.. so you don't have to bee glude to it all the time...
Maverick ET-73 is another very good one...has two sensors..one for the smoker temp...the other for the food temp...that is a remote one also...works good....I have one...
As far as how much charcoal to use, thats a hard one to give you a standard answer ...without a temp gauge...you won't really know...I would suggest getting a temp gauge and experiment a little first...before you try a smoke...
I would use a lump type charcoal.. instead of the briquetts...burns better...not as much ash to screw up the draft in the charcoal pan either
I would get 2 brikset cooks and 1 pork butt cook on a 20 lb bag of old style kingsford. I would add in some lump but never really measured it out to give you an answer. My rul of thumb for charcoal useage has always been less then 1/2 bag....go get some more. If more than 1/2 bag and some storage space.....go get some more.
To add to what others have said, I've learned that more isn't always better. I can get 225 with 3/4 of a chimney starter full of lump charcoal. If I use too much more than that, the coals smother themselves and I don't get enough temp. Good luck!
BTW, I use a vertical brinkmann charcoal smoker. I've drilled a couple extra holes and made charcoal grates to help with airflow.