Hey Chris,
I don't have that particular USB to Serial adapter that
@Katodude recommended but I do know that it works great because many are using that same one and it is the one that happens to be recommended on the github poolController web page.
I personally opted for the following adapters which also work (I just wanted to experiment with some different ones). The reason I like the following one is that it has power and status lights showing the traffic heartbeat between the RPi and the IntelliCenter RS485 bus.
Amazon.com: Gearmo Mini USB to RS485 / RS422 Converter FTDI CHIP with Screw Terminals and Windows 10 Support: Computers & Accessories
www.amazon.com
I also have the following one as well. However the "heartbeat" or activity lights are super bright. So if that might be preferred than this one works great also.
Buy USB to RS485 Converter Adapter 3.3V 5V FTDI CHIP with Screw Terminals and Windows MacOS Linux Support (White): Serial Adapters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
NOTE: Both of the above adapters are a bit "bulkier" than the JBtec (especially the Gearmo). If you've noticed, those RPi usb ports are very close together. So if you plan on using most of the usb ports and don't care beans about the status lights, then the JBtec might be the better option. Also, it's the least expensive I believe.
The RPi connects directly to the RS485 bus of the IntelliCenter via the USB to Serial adapter. so, yes the RPi becomes the host server. Those unreliable and funky Pentair IntelliCenter Prod Servers could blow up today (and they just might) and the folks that rely on the nodejs poolController /dashPanel UI instead, wouldn't even know it.

.....
For example; When I happen to see a notification from other IntelliCenter owners reporting that the servers are down (which you know occurs on a regular basis), I just glance over at my dashPanel web page (which I typically keep a window open on my Mac), or look on my iPad or iPhone and the dashPanel is just chugging along... No problem!!
r.
EDIT: Also, as kato pointed out, great idea to get you some more microSD cards. You will want to image your operational card and store that image on your desktop/laptop as a backup as kato recommended to me. Let me know if you happen to be a Mac user, as I found an outstanding method of imaging those cards on a Mac. If your a windows user then: Win32Diskimager works great I am told.
Here is another tidbit regarding the cards that I might mention...
I tried using a 64GB card initially and had problems with noobs etc. No issues with the 32GB cards. So as you start ordering additional MicroSD cards (and I have no doubt that you will lol), here is just one card that I happen to be using with no issues.