How much / what weight backing, for a wide-use 8 weight?

Hi all,

I'm normally a trout fisherman, and thus far all the rods I own are 5
weights and under. This Xmas I'll be getting an 8-weight set-up, to
use for, well, basically everything else I come across: stripers or
bluefish out at Montauk (or even from the piers here in NYC), small
barracudas and what have you down in the Keys, the occasional Salmon
trip (for example, out at the Salmon River in Pulaski NY), and Steelies
wherever.

I was looking at getting the Orvis Battenkill Mid Arbor IV reel, which
is listed for 7/8 weights... only, I see that when using an 8-weight
line, I'd only get about 100 yards of 20lb dacron backing.

I've read so much bad stuff about Gel spun being dangerous, and in fact
I already have the bad habit of letting my finger touch the line
occasionally, so I'm thinking I should stick with Dacron. But my
questions a

Is 20# heavy enough for the uses I mentioned (as opposed to 30lb)?
And, is 100 yards enough?

If the answer is no to either, should I maybe be looking for the next
size up reel, or a different reel altogether?

Thanks ahead of time for your thoughts...

Tim