Welcome, I think a lot of us have been where you are. As you said, these are luxury items. For sizing plywood, I don't think there is a much better solution than the Festool saw. Just start with the saw, another 55" rail, connectors and clamps. It's a big hit, and you may wind up wanting a panther or universal blade also for dealing with thicker solid wood and at least a Festool dust hose. I went years with only those things and eventually purchased a long rail and a couple aftermarket helpers.
But first, get used to using it. There are tons of inexpensive DIY solutions that allow repeatable rip/cross cuts without buying every jig Festool offers (example: one of my simple ones is here:
http://festoolownersgroup.com/festool-how-to/how-to-make-precise-cuts-using-the-ts55-and-the-rail-guide/msg4090/#msg4090). After a while you can decide if the Festool or aftermarket helpers are likely to provide a sufficient level of additional luxury for operations you do most often. A good cutting surface is a 4x8 sheet of styrofoam insulation on the ground. For quite a while, I used sawhorses with a few 2x4s clamped to it and a sheet of rigid insulation on top. Pulled the ply right out of the truck and onto the cutting surface. The rigid insulation is not 100% necessary, but it makes you not have to think about where the cut is made for support and improves dust collection by not allowing dust to escape the bottom of the cut.
In all honesty, I'm not sure I get my moneys worth out of the longer rail, aftermarket parallel guides, and other bobs and baubles I've added over the years relative to those early days. I think it's more important to develop your own process and add things thoughtfully than immediately empty your wallet and feel you have to use these things to be productive.
One example. It does take time to connect and disconnect the two 55" rails each time you want to make a long or short cut. So, the obvious solution is a long rail. Sweet right. Well, now you need to store a 9' rail. Where are you gonna put it? Then you have to spin and swing it into place in a small area when you need to use it. Now you need to do the same to set it aside for the cross cut. Time saved? ... yep. As much as I thought? ... nope. Same with the permanent cutting table that I have to push out of the way all the time relative to the one I only setup when I need it. Same with the parallel guides that take longer to setup than my cheap homemade versions, but get the rail into place way more quickly when used repetitively. All very minor improvements to get the same result slightly faster.
Hanging out here, it sometimes seems like you NEED everything to get any use out of your stuff. But, have fun and play with what you can afford. Remember that a significant number of the guys on this forum make money with their tools and that "slightly faster" means more to them than it does to me. What they consider indespensible, I consider nice to have. Just sip the green kool-aid as opposed to guzzling it [tongue].