Honwave air floor sounds perfect for your use. They are great boats and brilliant value. Every extra 30cm makes an inflatable feel bigger/safer and assuming you and or his mates will want to go out with him I'd buy within reason the largest you could manage. a 2.7 for sure or perhaps a 3.2 as they only weigh another 5kg.
If you bought used it's very likely a Honwave 3.2 would have transom wheels already fitted which would save the carry.
Bit like this outfit that sold for £650...
A 5hp should plane one up but probably not two up.