Outboard motor for dingy
We recently bought a Tohatsu 8(same engine as Nissan) for our AB 11.5 hardbottom. This 2 cycle weighs a reasonable 70 or so pounds.
I personally question that the environmental benefits justify the extra cost and weight of 4 cycle small engines - and would go for the 2 cycle as long as they are available in the US. You need to decide your own attitude about this near-religious issue.
As to size, you need to decide how fast you want to be able to go with how many people. I believe our 8HP will plane the AB with four people on board where I expect a 4/5HP may only plane with one on board. You need to decide what matters to you.
However, you might check on the availablity of parts/service overseas. I understood that the Tohatsu is widely sold overseas. I would wonder how widespread the global acceptance of 4 cycles is.