Sheet metal?
A 120V machine is fine for that. GMAW with C25 gas and 0.023 solid wire and off you go.
3/16" steel?
The only way a 120V machine can (reliably) weld that thickness is with FCAW wire. Sometimes using FCAW is fine, sometimes it isn't.
A 'small' 240V machine or a dual voltage machine gives you more capabilities on the thicker end.
BTDT.
Started with a 120V Lincoln with 'tapped' voltage control (not continuously variable voltage control). Nice little machine used within its limits. GMAW it can do 16 or 14 gauge just fine, while using Lincoln NR211-MP 0.035 FCAW wire it can melt right through 1/8" steel. But thicker than that (GMAW and FCAW) and I felt that the machine didn't quite have enough heat/power to give me reliable welds. I had some stuff that was 1/4" thick and really couldn't reliably get 'good' welds with the 120V machine, even with FCAW and no way at all with GMAW.
Got a 240V Lincoln (SP175Plus) with continuously variable voltage control. Much more capability and output power than the 120V machine. Still not a 'monster' machine though, anything 'thick' and I usually use SMAW. But it can do 1/8" to 3/16" steel with GMAW pretty well. And 1/4" to 5/16" with FCAW no problem.
IMHO, unless you are doing only small sheet metal type stuff, once you start welding and find out just how darn useful and fun it is, most folks rapidly outgrow the limits of a 120V machine and then have to go and buy at least a 'small' 240V machine.
YMMV and all that.
Just saw (yesterday, in fact) that Lincoln is doing a factory rebate on their PM210 machine. The rebate brings the price down to $999 for the machine. Not cheap, but IMHO a decent price for a decent machine. Dual voltage (120 or 240), and the machine can run some limited DC SMAW or GTAW as well.
Buy once, cry once.
Or get the 120V machine, learn on it and outgrow its power output limits and then go and end up buying a 240V machine.
(still wanting to get a PM256

)
Remember that you will also need a cylinder of shielding C25 gas and a welding helmet and welding gloves.
And also 4-6 angle grinders.

Yes, I put the chuckle in there, but you really do need some angle grinders. To use a flap wheel, and a wire wheel, and maybe a wire cup wheel, and maybe a 'hard' grinding wheel, and maybe a cut-off wheel. And changing wheels on the grinder back and forth during a project gets old real fast.
And you need a way to cut your project pieces to size and shape.
And some welding pliers (aka Whelpers). They're only about $10-$15, even for 'name' brands. But you really do want/need a pair. The Lincoln ones at Home Depot for ~$12 are decent. And cost the same or less than the no-name ones at Harbor Freight.
One of your first projects could/should be to make a welding workbench/table. Or at least go buy the HF folding welding table on sale for ~$60 (it's not bad at all, not great but not bad). Working on the ground *****.