Carpenter is indeed online! I would definitely treat the joists with a quick brush on of Cuprinol Green or similar (you can get cheaper products that are similar like "Panabond" or "Larsen"- they all contain copper sulphate AFAIK). At the very, very least you should treat all cut ends and any endgrain and especially where you may have cut/ chiselled or otherwise worked the wood. It won't take long and you'll have the satisfaction of knowing that you're deck is going to last. A little tip for you- you'll need two drills for fixing down your decking, one to drill pilot holes and a driver to drive home the screws. Rub each screw thread on a bit of candle wax and you'll sink them extra easy and extend the battery life of your drill. Some of that treated timber can be rock hard and is hard work with power tools. If your timber is CCA treated (not so popular now I believe) don't burn the offcuts in your fire- it's hazardous waste. A chalk line and some speed clamps are your best friends for this job. Good luck with it, you've got the weather on your side anyway.