first limit is your electrics, what can it handle (don't max it out). second, physical space and accessibility, how big can the appliance be on the outside. frontloader are nice but almost twice as expensive (here at least) and of course what size works are you realistically making, and how much. A kiln shouldn't stand around unused for months at a time.
I just got myself a new pyrotec kiln (I'm in Germany), it had 36 weeks delivery time. My old one was an ancient smaller front loader, and while it was fine as a first one, it was pretty EOL and affected the outcome of rhe firings a lot, but it was too old and crumbly to refurbish. I did put in a new controller (bentrup tc66) and a new thermocouple and that just works. On my new kiln i went with the TC75
while it is probably possible to program you own PID controller and the power electronics with the contactor, I would advise against this if you are not knowledgeable in electrical engineering, and kiln building is a different hobby than pottery ;-) Also your home insurance might have opinions one homecooked heating appliances.
From the intro/training when the new kiln was set up I've learned that most used kilns are more abused than they look (microcracks from opening too early, while still above 50C etc, these things are not fixable). If you can afford it, I'd say go for new. it'll last decades with proper care and maintenance.
I'm not familiar with the Skutt models, only know the brand name from online articles and shops here don't carry them next to the multiple German brands.
For me the decision against building my own controller was mainly because I wanted pottery as a functional hobby, not kiln building. But it's only a big toaster oven in a way.
Kilnsitter control where you need a pyrocone to switch off are not common here and a recommended against for safety concerns. I'm very happy with the controller I have now.