I fish off a 3,5 metre inflatable in South Africa. We have a couple of small boat builders here using hypalon to build tough-as-nails inflatables. The wind is a factor so I suggest you invest in a hefty trolling motor and two good deep cycle batteries ie. rather get two 50ah jobbies than one 100ah - its just more sensible to have a backup in case one dies. The extra anchor suggested is a good idea. PFD's are also a must, although they're of little use here as we have crocodiles and hippo's, if your boat sinks you're food.
Keep a patch kit handy on the boat. Pre-cut patches in various sizes so you don't have to fumble around when you have to do a quick patch job on the water. Never leave your hand pump on the bank.
The most important thing about inflatables - especially smaller ones is to keep them tidy at all times. It's often a bait knife or a hook lying around on the deck that causes a puncture and when the chips are down it will be the anchor rope that was all over the place that drags you under.
Invest in portable electronics. Marking a slightly submerged tree stump or rock on even an old second-hand gps with an alarm will keep you out of harms way. I have a small barometer that tells me when there is a sudden drop in air presure. It means its time to get off the water or at least move closer to safe access to the bank as windy conditions are only a few hours away.
good luck and enjoy the fishing