Welcome to the FOG.
Platform - Since most of my work is site-based, I’ve always personally tried to keep everything as simple, robust and collapsible as possible. So for me - it’s a pair of Toughbuilt trestles/sawhorses with two sacrificial 8-foot 2” x 6” battens laid on top to support the sheet. The trestles fold flat and take up almost no space, and the battens can be laid or stood up wherever there’s room.. Simple, low-cost and effective. Although the STM has its fans on here, it’s a crazy-expensive way of having something to rest a sheet on compared to the above. Just my opinion obviously, but in the UK you can buy a TS55 and a CT26 for less money.
Saw - the TS55 is really a game-changer when it comes to sheet goods, and it will deliver very accurate cuts. Once you get into it, you may well find yourself using your table saw much less. Pretty much the only task mine ever gets used for these days is for repetitive cuts of multiple items which have to be exactly the same size. The corded version of the saw will cost substantially less, and would be my suggestion if you don’t plan to take it out in the field too much. I hear great things about the cordless version though - so go for it if you have the budget.
Rails - these come in a whole variety of lengths as you’ll be aware. The longer ones are initially attractive for longer cuts, but my personal reality is that they’re a pain to store and can be cumbersome unless you have plenty of space. I use 2 x 1400mm rails joined together for 8’ board cuts, plus I also have a smaller 800mm one for 4’ cuts. The three rails give me the ideal combination of length, flexibility, convenience and capacity. Here in the UK the TS55 is available as a kit including the 2 x 1400’s plus a pair of rail clamps at a price which is less than the cost of the individual items. Maybe it’s the same in NA, I don’t know.
Other stuff - you’ll need a pair of rail joiners if you decide to go down the above route. I actually have two pairs, so all three rails can be connected together for a 3-meter cut. An almost mandatory accessory is a TSO guide rail square - this device clamps to the rail and ensures square cuts whilst breaking down your sheets.
You’re maybe also going to need some dust extraction. Many, many useful threads on here. The search box is your friend. Hope you get fixed up.
Edit - it’s a good idea to include your location on your profile. The FOG is a global community, and not all Festool products are available everywhere. It’s way easier for members to give advice if they know which country you’re in.