No matter how you look at it a portable is a pain. Like many here I started out with a portable. A US Products Solus 310. I ran 25' of 1.5" hose with a 2 jet
Evolution wand.
In the beginning I was always thinking I needed more vac and psi. But I learned that with proper wanding my dry times were just fine. As far as psi I found that 310 was more than enough with proper chemistry and agitation.
A 175 does wonders for portable users. I would use it to agitate my prespray and post bonnet after extracting. It completely changed my game and results.
I would also recommend that instead of getting an inline sprayer, you get a battery sprayer like a Multi sprayer or a SOS Gentoo. I have found them to be much quicker than a inline, especially if you have a limited to hose run. An inline also uses up your freshwater supply. Adding water and dumping water really cuts into production. I know you wanna run auto dump and fill, but it's not always available.
My recommendation would be to run whatever portable you can get for the cheapest and then move on to a truckmount. There's some really great deals out there.
I know a van can be an added expense, but depending on what your location is a trailer is a great way to get a truckmount without the added expense of a van and insurance. You can use your personal rig to tow it and also use your vehicle as a tax deduction. You can store all your equipment in there as well. It's like having another garage. If you live in a huge city where parking sucks than a van is a better option.
In carpet cleaning everything boils down to efficiency. If it isn't going to make you more efficient then you don't need it.