If you separate the mashing and lautering steps from the boil, there's no reason that a partigyle brew day would be any more complicated than doing a single beer... In fact, it'll make your math easier. It'll just take longer. Plan on basically a full day to pull off your first AG double brew session.
Have a couple of buckets on hand to collect second (or even third) runnings. Note that plastic carboys won't stand up well to the ~150F heat of the wort (and I have a warped BB to prove it!), so you need buckets or extra brew kettles to make this work. Then just collect your runnings and boil at your leisure.
Later, as you get more experienced, you will heat the wort more quickly, likely with sparging, to stop enzymatic action promptly and get a more predictable brew, but for starting out, just collect the runnings as they come and don't start the boil before you're ready. You might even decide to clean out the MLT before starting a boil. That's totally fine for now. We're really splitting hairs here. Will it be the best beer you can make? No. But will 1 in 10 hardcore brewers or 1 in 5 BJCP judges be able to spot what you did? Probably not. It's a small issue, really. And it's not a fault, really.. it's just a deviation from a repeatable procedure. Your beer can still be fantastic. And hey, it's your first brew on your new system. So just go for it.
In Process: Mango Beer, Homebrewers Pale Ale
Bottled/Kegged:Spicy Light Rye, Rice-adjunct Pale Ale, Mild Bourbon Porter, Roasty Stout, Basic Light Mead, Bourbon County Stout Clone
Up Next: Berlinerweiss, Chocolate Raspberry Ale, and American IPA