Pete. Welcome to the forum. HAve you filled in yopur profile !!
Good choice of first boat. You need to get a plan really, will solve a lot of questions.
What scale is the boat? A bit of surfing should find out what size are fitted to either the real thing or some commercial hull and you can go from there. As a guess 40mm ish would be ok for a boat that size.
Motors and I would reccomend a pair of 555 from, say, model motors direct, or even a pair of MFA 540/1 …both choices running on a 12v Gel battery (SLA) of 7Ahr..this will give you some ballast as well (but check the waterline with weights before buying!!).
Ashley