Right on dude! I have the 110 lpi and 195/200 lpi which I bought from a local printing supply company. Bubbleman markups are ridiculous @ $100 per screen and Pocono doesn't ship to my province.
Those are the 2 basic screens and all you need to get started. 110 to separate headies from the plant, 195 for the static sifting or carding. No need for upgrades but more screens in the system never hurts. I may pick up a ~60 and ~90 some day but haven't found the need for it yet. My only tip would be to get the largest ones because mine are just under 2ft x 3ft and I find myself wanting more room. Also if you get really into the sifting you might want to purchase a 2nd and possibly 3rd 195/200 lpi so you don't have to clean the screens as often - That is if you're after the 99.9% heads purity.
If just using them for trimming the 2 screens will serve you just fine and you will get a very nice product with little to no effort to clean it up.
Bubbleman's 4 screen kits consist of 60, 90, 110 and 200 lpi
Cuban grower uses 61, 86, 125 and 180 lpi from Pocono for his award winning sift
Hope this helps!
You planning to do some dry sifting or are you just wanting them mainly for trimming?