Yes on buying what you want now, especially when paying for a special order. And, yes, it depends on how you will use it. We are full time so our needs are a bit different.
I would get all the insulation stuff I could, including dual pane windows. Also get as many A/C's as the unit will take.
Are you going to upgrade your truck? If not then you will be limited on which units you can get based on payload. Especially important if you want a generator installed (a lot of the genset weight goes to the pin).
If you plan on boondocking with A/C then a genset is needed. If you have one installed (propane) then you will need more fuel capacity (buddy tank or larger onboard). One thing good about toyhaulers is most have an onboard gas tank that the genset can run from.
We full time and have not had a reason to have a larger refrigerator or tankless WH. But, neither of us takes 30min showers either. We found that shopping for food more frequently leads to less waste, so the smaller refrigerator actually helps us meet that goal. I must admit that we have a second refrigerator in our outside kitchen where I keep our extra drinks. That is worth every penny. Never use the outside kitchen for cooking, just storage. PS the outside refrigerator is 110V only and it will not keep food cold during a day of driving in the summer.
Auto leveling would be nice to have, but, they can cause ground clearance problems at the rear. Make sure the trailer will ride level with your truck. Ours just has the rear stabilizer. It is a little more of a pain to set up, but, since we usually stay in a place for more than a few weeks at a time it is not much of a problem. When stopping overnight I rarely disconnect the truck. If you do not get auto levelers then some sort of stability system is needed. I got the JTstrongarms, which work well. There are other cheaper solutions that just take more time to setup (like cinder blocks
).
Slide toppers do help in the summer. I will probably get some installed on my trailer in the next year or two. I will get the ones that also work as awnings for the slideout windows.