Oh well fella, it seems you have opened a can of worms here on UKgser. Getting hot on a hot day can be dangerous as far as riding a motorcycle goes with the concentration and dehydration and all that. Not that it bothered me when it is really hot. You see I'm from a geographical location where hell is a cold place to go to before I ended up on this island. 1st things first, be comfortable, 2nd stay hydrated, 3rd it is better to have a siesta in the shade when it is warm and the sun is baking down than riding a bike in the bloody heat. So plan your riding around the part of the day you know it is going to fry you.
My experience as far as this goes is as such. Going into town then flipflops and t-shirt is appropriate. The kids on the scooters ride like that for a reason, just don't ride like them. When out and about riding the best roads, bin the jacket (rokstraps is worth their money for this other than securing a Tesco bag), keep the trousers on if only to cover up the carpet burns. Keep some water in the tank bag that you occasionally douse yourself in (top tip, pack just white t-shirts for the missus) and take a few sips as well. Wear the gloves cause getting the wee man out for a hmmm wee with broken fingers is not fun. The boots. Here you will wish that you didn't buy the unstoppable premium German product. No matter what you do your feet will feel like a corpse in a Nazi oven which is exactly where they will be.
The hand guards can stay (it will ruin the looks if you take them off), you need the perspex to keep the beetles at bay or out of your face, you are a bit fucked because Ride Rider Survey has voted the GSA as the bike with the best wind protection. It is an adventure (don't ask what an adventure is cause that is a 12 pager at least) so go and enjoy, experience it and when somebody else ask a question you know the answer to then tell them or don't. They will find out soon enough.