Replying to SKIS!

Heeeeey NS, i need your help on a n00b question.

I just got started park skiing this past season and now that the end of summer is almost upon us it is time to get off my crappy old skis and buy some new ones!

Since i have a fairly low budget, i was kind of leaning towards getting a pair of the new silencers. My first question is, will these skis hold me back as i progress more and more? My second question, what size to get? I am somewhere around five foot five to five foot seven and like 115lbs. The silencers come in 149, 159, 169, 179.

Ok third question, ill probably get some hate for this one...
Where should i get them mounted? I know that everyone is going to say CENTER MOUNTED DUH NOOB but some of my frans i ski with reeeeeally suck at park so we ski groomers a ton. Will it greatly hurt my park skiing if i get them mounted a lil back? How far?

Thanks for the help, i really need it.