If you want to replicate the capability you used to have with the "3 big welders" in your former business, but are now confined to a residential home garage, the first issue that comes to mind as far as machine selection is input power.
Do you have 3 phase power available, or like most residences, is your service only single phase?
If single phase, then it is important to scrutinize the output specifications for machines that are promoted as working with both 1 and 3 phase input power. Those machines are often advertised, and named after, their peak output power while on 3 phase... but on closer inspection of the specifications, we find that the peak output power on single phase power is substantially less. Or even when the achievable amperage is the same, the duty cycle is significantly lower with single phase input power.
The ESAB 285IC for example, is rated at 200 amps, 100% duty cycle on 3 phase, but is downrated to only 160 amps, 100% duty cycle on 1 phase. At 60% duty cycle, which is where many brands of welding machines are compared, the 285IC is rated for 265 amps with 3 phase. Not bad. But the 60% duty cycle is downrated to only 210 amps on 1 phase. I'm not picking on ESAB, I'm just using this particular welding machine as an example, since it was specifically mentioned in the posts immediately preceding.
When I shopped for a multi-process machine for my home garage, like many, I was limited to only 1 phase, 230V. To bring 3 phase to my house would cost over $100,000.00, so that wasn't in the cards. I specifically looked for the highest output amperage rating for the longest duty cycle available with single phase input power. At the time I shopped, there was only one power supply available on the market that clearly exceeded all others in the amount of available welding current and on time on 1 phase, so that is the power supply that I bought. Sure, it happened to be built with a few bells and whistles to go with it, but the motivating decision was the output power and duty cycle on single phase.
If looking to weld 3/8" plate, as the original post states, and also looking at doing Mig and Stick, and are confined to the limited space of a home garage, and are also restricted to single phase input power, then the highest available welding output amps at 60% duty cycle on a CC/CV machine that I am aware of is the Lincoln Power Mig 360MP, at 320 amps. The older, more traditionally designed, but still available Power Mig 350MP is 300 amps, 60% duty cycle. Both of these machines are CC/CV, so stick welding is well within their wheelhouse, along with push pull, pulse, "pulse on pulse" for "mig like tig", a dynamic "Power" mode, synergistic or independent wfs/v control, and a host of fine tuning features like arc, inductance, and trim control; pre and post flow gas control; start procedure settings and duration control, for hot starts or cold starts, with ramped arrival to the weld procedure; separate run in wire speed control; separate crater and end procedure control, that is also ramped; anti burnback control; a spot timer; a crisp arc and a soft arc for user preference per the flux coating on stick electrodes; dual shielding gas inputs; spool gun capability; and it can DC TIG as well, although that isn't a process you mentioned wanting to do.
Setting all those features aside, however, and just focusing on available welding power, and the ability of the machine to thermally manage the output (hence duty cycle), I have yet to find a machine capable of both GMAW and SMAW that has a 60% duty cycle rating of higher than 300 amps on single phase. And that alone is worthy of consideration, if heavy plate is on the agenda. The other thing to consider is that this machine isn't new. It has been in production for 20 years now, starting as the PowerMig 300 in 2000, and changing names in 2005 to the PowerMig 350MP when Miller introduced their MillerMatic 350P, due to the perception that 300 must be less powerful than 350. Since the PowerMig 300 was already capable of 350 amps, changing the name to 350MP did not involve any change to the input or output power specifications.
The newest Power Mig 360MP, however, is built on an entirely different platform (not just a label change), and does offer a little bit more power than the long running PowerMig 300/350MP. Currently, one can choose the 20 year proven 350MP platform, or the newest state of the art user interface of the 360MP platform, for the exact same retail price. It is interesting to note that the older model is not only still offered, but it is the same price as the newer model.
Anyway, if anyone knows of a multi-process power supply that can produce more welding current for a longer duty cycle on single phase, post up about it, as a comparison would likely be of interest to anyone shopping for the most available welding output when limited to 1 phase.