Sailing the Nacra 5.8 one up won't be the problem, righting it one up when you go over will be a problem, you can overcome that with a proper righting pole, not one that comes from under the mast step you need one that comes from inside the top hull as in Rick Whites righting pole he sells on this site and it will be a long one. When you sail in the ocean and go over generally there are waves coming past that help lift the mast and start the righting process, on a lake with two ft chop it is harder, if it's light wind even harder. To start sailing a Nacra 5.8 solo, that advertised boat is a good option as it has the small jib, tie your sail battens in loose with a wrinkle, then pull the downhaul on really hard (the main sail is made to stretch and a good crew can pull the bottom of that old sail out of the bottom of the mast) so the sail also stretches out over the battens and goes as flat as possible. Sail with your boards quarter to half down and it will steer fine. If it's light wind the Nacra will steer OK with six inches boards down. The Nacra 5.8 has no boom so if you get in trouble and let your main sail off too far it just bags up a bit and is more likely to help tip you over, you need to try and keep the jib and main sail on hard while learning and just steer up into the wind as each bigger puff comes, set your cleat so that you can only cleat it if you pull the main sheet up high so you can cleat when you do your jib while on the tramp but at all other times you don't have it cleated. Over 12 knots plus gusts you must get on the wire or it will be a busy ride. The big advantage that old Nacra has is it's heavy so it handles some of the gusts for you and gives you time to react, on smaller boats you need to balance the boat by your position, a Hobie 16 is a good example I'm not bagging them but in a puff too much weight back you go over backwards, too much forward and you go over forward on that Nacra sit where you like unless your going flat out the only way you will go over is sideways. When you take out inexperienced people you have a crew so the 5.8 will be easy to right easy to sail, tip the boat over in the shallows and right it with them so your all confident and when the boats going over tell your crew to grab a rope as they slide down the tramp, never climb to the high side when it's definately going over or you will put your mast into the mud, get everyone to keep their legs together as you go in the water, getting a leg either side of a side stay can be uncomfortable for a long time
I wouldn't worry about having the same cat as the others too much, as long as you get a cat that still has new part supplies you will be fine, Nacra has all the parts a phone call away and any tuning help you need can be sorted with a post on this forum