Welcome to the forum.
A 5.5m SIB is a seriously big boat for a SIB. To give you some indication of scale take a look at this Zodiac MK V (5.9m). It's an HD aluminium floor and can take 90hp. It's overkill for what you need (Milpro) and is built like a preverbial s**t brick-house. This can't be dragged with a 40hp on the back.
As you've bought the engine already, then I'd be inclined to look for something around the 4.5-4.9m range. Boats such Zodiac Fututra MKII to MKIII will fall into this bracket. You can choose between air floor, ply or aluminium floors. All well built and suitable for leisure market.
Double-check before purchase because the new ones now take long-shaft engines.
Avoid cluttering the boat with seats and remote steering and use the inflatable tubes to sit on. Then add in fuel tanks, probably 25 litres tanks, or two, safety gear, wet weather gear and camping kit. It'll be tight with 5 on board, but workable.
You really need to see one up close to visualise, see what's involved to break down and pack, assuming you will build when you get to the water. Normally 2 bags with boat in one bag and floor boards, stringers and oars in the other.
Note: carrying 4-stroke engine requires powerhead to be higher than leg and has to be laid down on a certain side.