I recently asked a similar question regarding my AF Servo and focus points on my 60D (HERE).I think you'll find it can select any single point, or all of them , but not groups - as far as i'm aware out of the canon range only the 1 series DSLRs (and maybe the 5d etc) let you pick groups.
read your manual
that said for most of the photography you are going to be doing there's no need to have a group selected anyway - if the subject is stationary use one shot a single point, if its moving use servo and use them all - simples
There a few posts in the link below which might answer your questions and help you decide .Looking at buying one of these in the month or so. Quite surprised there's not more said about them on here.
This is the one I was thinking of getting http://www.digitalrev.com/product/canon-ef-s-18-135mm/NzUyNg_A_AOriginally Posted by Immaculens
for the 18-135mm - you need f/5.6-f/8 through the zoom range for optimum IQ
The 17-85mm seems to outperform
maybe save for the 15-85mm is you can
all 3 lenses have some major barrel distortion at the widest ends.
Yes I read about that but sadly it's also twice the price and a bit out of my budget at the moment.thats the older version of the lens
this >>>>> http://www.digitalrev.com/product/canon-ef-s-18-135mm/MTAwMDk0MA_A_A is the newer version that is apparently far better