The question is though... how do you get a link up on a PR7 site? It´s not like you can just go ask a webmaster... yo, put up a link for me? I´m pretty sure that you´d have to offer something in return.
You can buy them if you have the cash, or see if you can do some kind of link exchange if you run other websites. I can say too that if you get a lot of links to a new site you will suffer in rankings for a little while. I'm at this stage now with a new site of mine, but I expect in a few months that my rankings will be good! I only built about 1000 links over a week or longer, so as long as you don't go overboard and try adding that a day you should be ok in the long run. Fingers crossed!
If you are worried about being penalized for having too many backlink's, try only linking with quality ranked websites (as mentioned before). Also, as long as you don't use any backlink application or black-hat linking method, I'm sure you'll be alright .
Just keep the number of link increasing pace reasonable . It is safe even you have many links. Plus offpage factors will not have too much negative effects for your sites.
Yes, if you build links too fast it can get you flagged, by Google at least. It's viewed as an automated method of link building. Slow and steady wins the SERPs.