I guess this might be a bit redundant now that you have got the bags and rack..... but i recommend a rack that is more square at the back of it, it helps keep the bags from bending into the spokes, unlike the races that are straight metal from the back rack to the frame hitch place.
I hope you enjoy your backpack free cycling :)
When they are fitted and loaded get down and have a look underneath to make sure they don't rub on anything. If they do best to get in early with some gaffer tape or something to protect the bag rather than (like me!) do it after there is a hole. I've got axle bolts on my commuter so more to rub.
Do they grip the top rail or might they come off in a bump? Usually takes a very big bump but worth remembering if that can happen so you don't leave one behind!
I bought some bright yellow, elasticised waterproof covers with reflector strips for mine (off eBay).
They fold away very small and offer both (some) protection from rain as well as a high vis safety element.
Also, being basically untrusting, I have a small plastic covered wire lock that I twist around the handles and carrier rack when I go into the market.
Torpedo 7, where he bought his panniers, also sell yellow covers.
I am in the market for panniers and online shops are cheaper, but I would like to hold them up to my bike and rack first. One online store sells interesting waterproof Tioga panniers in black and reflective grey. Yellow covers would be more visible. Another downside is no pockets to store extra water bottle or wet towel.