Looking for recommendations on which functional, as opposed to aesthetic, options to get and which aren't worth it when purchasing trailer?

I guess all depends on what and how you plan to use it. For example the battery will last you a few days late in fall using a little heater when going to bed. You plan long trips off the grid and must have 110V for whatever appliances than you need the converter and solar panels. Talk to Steve and trust him; he will ask you the same and will not suggest you to buy stuff you don't need. We for example have a camping folding table so we didn't opt for the table. But I bought the spare full size wheel just because I've seen plenty of tailers - not this type - with flat tires. I choose the large size tires because is a better choice overall. Didn't choose the water system with sink and pump. We use the blue 5 gal. reservoir and just flip it when needed. Again depends on how much outdoor person you are or prepared to be. See my picture for our configuration. Happy trails.

My experiences (primarily for use in Provincial sites with no power)

We went with 2 batteries mostly for the purpose of keeping our small 'real' refrigerator (AlpiCool) and the need to run my CPAP machine.

In hindsight the sink and pump were not really needed for us.

I have plenty of solar in addition to 1 panel on top so I can park the trailer in the shade and run a panel via a long cable to the battery.

Most if not all of our devices are rechargeable and they are fully charged when we head out. e.g lights and USB power packs

The roof rack was a great option to add on to (awnings and cargo carrier)

We love our side table as an additional prep area.

Large tires and spare were a no brainer for me and I love the larger tool box on the front. Also the prewired upgrades are a good consideration.

Hope this helps