I'm getting a little fed up with the sweaty back syndrome on my 12 mile each way commute from carrying my work clothes and stuff in a backpack, so I've decided to invest in a rack and a single pannier for my Kona Jake the Snake. I have quite a few questions though...

Been considering Tubus racks, but not sure which to go for, their stainless steel rack costs a third more than their other steel racks but it'd be more durable and corrosion resistant. Also, are the fixings universal for all makes of bike that have the lugs/thread braze-ons as part of the frame, like my Kona has? Are there any possible screw/thread incompatibilities?

I've been considering Ortlieb rack-mountable bags, like the Back Roller, but I'd only need one, rather than a pair, for my stuff. Alternatively I've been considering a backpack that can be rack-mounted, like the Ortlieb Vario, for those times when I'm using the bag for short trips on my other (folding) bike which cant' take panniers. Are such convertible bags worth considering, given that they cost loads more?

Basically I'd looking for feedback and advice from any others out there who have a rack and panniers on their road/commuter bikes to help me choose the right rack and luggage combo.

TIA