Re. the weight thing you need to check multiple manufacturers - a given horsepower of engine will share the main lumps of hardware with one or two other HP variants.(probably more at the 3 figure HP end of the range).
Net result is you could have ,say an incredibly heavy 70Hp from Manufacturer A, whereas the 70 form Manufactureer B makes revery other 70 look lardy.
A's engine is a de-tuned 90/ 100 lump, wheras B's is de- tuned to be the 60 & the 50.
So as you are looking in the 90-135 range you may find someone's 130 is not a lot heavier than someone else's 90.....
As for fuel consumption have a search on here - the general average regardless of engine size or strokes appears to be about 1 L/mile. Yes if you do a lot of low speed / idle work (e.g fishing) then go fuel injected 4- stroke. If you blat along at WOT all day at WOT then it's a case of if you need the gee gees you need to burn the fuel!