I toss out all link requests that...
1: ask me to link first
2: tell me they linked to me, but if I don't reciprocate in some number of days they'll take the link down
3: mention PR
4: tell me how much the link from them will help me
I'm most likely to seriously consider link requests that look something like this...
I own (some business) and we sell (some related product) and wonder if you would link to my site, it's (some web address)
There are more factors, but these relate to the actual link request email.
As far as pace goes, actually looking at the sites you might ask for a link should pretty much limit the speed of requests sent out, assuming you are doing it all yourself and other site building activities take some of your time.
Go for quality rather than quantity. make a list of target sites, prioritize them for desirability, then start sending requests at the bottom of the list and work your way up. That way you'll get a chance to see what works best for you before you burn through the most desirable target sites.
Of course that assumes you don't send the whole list at one time.