From Abisko you can either go south along Kungsleden - spectacular scenery and fairly easy walking, but a bit of a pedestrian motorway, even in August. Big, staffed huts, but you can camp otside and use the hut facilities (cooking, shelter from rain etc.) for a fraction of the price of sleeping indoors. the huts have food for sale, too, so you don't have to carry so much yourself.
Going north and then east from Abisko takes you round the "northern cap" (nordkalotten) route, along the Norway-Sweden border, ending at Kilpisjærvi in Finland. Huts are small, unstafed and have no food, so you have to carry about 10-12 days worth - a lot at the start. Commercial groups use the huts, especially in August, so they can be very crowded - best to camp.
Continuing from Kilpisjærvi and ending in Kautokeino is worth while too, especially if you take in the Reisadalen gorge, one of the fantastic secrets of arctic Norway.
Insects not generally too bad a problem in August - much worse in June and July, but have tightly-woven clothing and take mosquito head nets, just in case.
We had no problems in finding alcohol for our trangia in pharmacies in Chile and Ecuador. You might find gas canisters in outdoors shops in some of the biggest towns in Chile, but I wouldn't rely on it.
Also, you'll probably be at fairly high altitudes in some countries - Boliva especially. Make sure your chosen stove can cope with that.