You are not too heavy to helm, bearing in mind that good cat sailing takes place in heavy weather when your height / weight would be an advantage although in light airs you'll be overtaken by lighter crews but that's the same for any class or type of boat and it depends weather you are planning to buy a boat with an asymmetric kite or not.
As far as experience goes it does not matter to much because getting the hang of cat sailing is easy insofar as they are more stable than monohull dinghies in all but the heaviest of weather but you need someone to show you how to trapeze off a Hobie as the method of "getting out" is different from dinghies and juggling the tiller, trapeze and when necessary, the mainsheet at the same time without injuring yourself or others is an acquired skill.
Sailable Hobie 16's can be picked up from as little as around £1500 but the more you pay the better the boat and the more likley it is to be competetive, as the hull weights are unpredictable for older (and heavier) boats.
The sails are known for lasting the lifetime of the boat as you are unlikely to stretch them as they are v.thick material... but some people are picky and will change them after a few years. You also need to be aware that a new mainsail is around £1000.00 to buy!