Do yourself a favor and don't bother w/Slime. Been there, done that and it proved to be worthless and messy. Get a pair of Schwalbe Marathon Plus 25 or 28mm depending on what your loaded weight will be. Your problems are over. I've got over 12,000 miles on a set of 28 mm w/one flat and one slow leak in 3 years. Also, Mr. Tuffys w/a high psi tire is an iffy combination as well. You'd be better off w/just the thorn proof tubes. If you don't have the clearance for SMPs forkwise get a Marathon for the front and an SMP for the rear.

AFA as the weight aspect goes one doesn't notice it so much when the object is to arrive at a specific place at a consistant time. Commuting isn't the same as road cycling/touring/utilitarian where one has time latitude. So, if you're a 20 mph rider you're going to be frustrated unless you dial back your expectations to a more realistic pace for commuting. 15-17 loaded is even a little high. Give yourself an extra 10-15 mins for flat/clothes changing time. Don't ride in your work/school clothes and don't work in your cycling clothes.

A seatpost rack/trunkbag combo is good for tools, lunch, etc. Get good lighting as well. 2-3 blinkies for the rear and 2 headlights for the front. One for seeing(Niterider Mi-Newt 200 for example)and one w/a blinking mode for daytime travel. Welcome and have a great time tailoring your rig.

Speaking of tailoring as you live where it rains alot full coverage fenders are a must as well as mudflaps front and rear.