Newbie Salmon ?'s (for next year)

[nitecrawler128]

Long story short... I bought a new-to-me-boat that is set up to Salmon fish, but have no experience Salmon fishing. I'd like to maybe give it a shot next year out of Esky/Ford River area if I can peel myself away from walleye fishing. I'm bored today and was looking on e-bay for cheap leadcore (found some!). Looking to spool lead-core on Magda Pro 30 reels. My questions are...
1) Do 18# and 27# run the same? (If I remember right, 5 feet per color at 2mph, so all 10 colors gets down 50FT?), or does the 27# run deeper?
2) Is 20# mono what you guys use for backing?
3) Does anyone know how much backing I can fit on an Okuma Magda size 30 reel with 10 colors?

I'm thinking if the 18# runs as deep as 27#, to go with that to save on reel space, and I could maybe fit 450 feet of 20# backing???? But like I said these numbers are shots in the dark; I don't know what I'm doing If anyone reads this thread that could provide me with some insight before July next year, it would be much appreciated. Thanx!

Forgot to add... A Magda 30 Reel holds 340 yds of 20# dia line. An Accudepth 47 holds 300 yds of 20# dia line (if this helps to answer line capacity ?'s)