bigger motors faster they go :) I'm currently building a huntsman cabin cruiser that will run twin props i will be working up to twin Graupner 800's but will start with my current spares 2 540's.
difference betwee brushed and brushless motors is that brushed motors offer better performance but at a price to regular brush replacements at cost £5 a set for good quality.
Brushless well thats answers itself good all round motors less maintenance but will heat up a lot not only the motors but the battery's too!!
what size is the cruiser?
36", 48"? bigger? for either of these sizes a 700 would be more then adequate to obtain a nice plane 800 would achieve it better.
if your going to use twin props
possible use twin 600's twin 700 or 800 ''MIGHT'' be a tad insane and very unstable on the water.
depends what you want to achieve i guess a nice smooooooooooooooth plane reasonable speed go with the 700 or twin 540's - outright speed go with the 800 or twin 600's maybe 700 if your sure you can control it
remember using 700 or 800 motors you may need a 40 amp esc check motor requirements but typically you looking around the £50 mark for 1 esc, 600's would normally need the 25 amp esc at £25 there abouts so if costs a deciding factor bare this in mind ...
also if your using twin props and rudders u will want to concider the use of a v tail mixer to help with turning (actions P40c).. adding a further £27 to the budget...
check out actions website for details on esc's mixers etc...
I would personally recommend Action Esc's and mixers or for the twin prop and mixer system Actions P94 that does all the jobs in one go ... but at a cost of £78 and only can take 20A so your limited to max of twin 540's ( please correct me if im wrong there)
http://www.action-electronics.co.uk/mixers.php