"Blah blah, descend and maintain 3,500 feet until established with the localizer...etc"   my questions derive from the clearance.     First, is the localizer, how will I know when I establish it?   I assume it's when the glideslope becomes visible; and if it is that, is there a way to find where this will happen before I reach it?

And second, the 'descend and maintain' part seems to be rather low all the time.  Occasionally I'll near miss a mountain or something because the altitude they told me to maintain is low, and others I'll be hovering above the ocean for a rather long time before the airport runway comes to view.  Is this supposed to be a very slow descent, in relation to reaching the glide slope at a higher spot?

Any help is appreciated  

"established" refers to case break - or when the needles start to move.  Once they begin to move you descend to your next altitude. 

You don't begin the descent (if you are doing an ILS) unless you are at the glide-slope intercept altitude.  At least in real life, there is a "false glide slope" which can deceive you if you are at the incorrect altitude.