Welcome to the forum!!!
First, got to this website, gives all the models and somedifferences in the Sears GT's way back when.
Ok, here we go....
The ST/10 tractor is called a "custom" . They were built as a more lower entry type line, still a GT, but lighter frame, light front axles, usually lower HP. Also one big drawback to the customs is because fo the front axle, you can only use front implements designed for hte custom tractors. The 3 pt hitches/implements though will swap between all the tractors.
The larger ST16 is a heavier built "suburban", heavier front axle, frame, rearend and the mid to later 70's tractor all had higher Hp ratings. You can also swap the front implements from about any year starting in 65 or 66 on up thorough 79, blades, snow blowers etc. Much more plentiful and you wil have a much easier time finding them vs the custom implements.
Someone also mentioned the SS tractors. In the mid/late 60's this was just small upgrades, woodgrain dash, longer footboards, wider tires. In 71/72 that had a two yr only run of a 14 ( '71) and 15 ( '72) horsepower Briggs. In '73 they went to the yellow/white tractors and began adding larger motors and also the Twin Onans. After 73, the ST pretty much single cyl, the SS meant twin.
If you can find a 73-79 SS in good running condition, grab it.
Other than the Twin Onans, and the two Briggs years, All Sears used some variation of the Tecumseh motors. Flatheads up to '72, then the switch to the newer Overhead valve design. They also introduced the "SSI" or solid state ignition in late '67. The module can burn up, 40 yr old used evilbay ones are outrageous, but there is new modern day parts to replace them so not an issue anymore.
Since Tecumseh went out of business, rebuild parts are getting hard ot find. Ebay has become source of most use parts, but prices are getting crazy. The twin Onan parts are also pricey, but still pretty readily available.
The OH160 motor in the ST16 is a decent motor when running, but are prone to the module burning out and also dropping valve seats, usually exhaust seats due to heat variances. I have a '77 and once I got a few thing fixed, I really enjoy the sound of the single cyl and I've never stalled it before I lost traction.
I use both snow blower ( on a '96 craftsman) and plow with my '77. I prefer to plow just cause the blower is old and worn and I'm constantly fixing on it. Now I will say I sure do like blowing the snow out into the yard or away from drive, but prefer plowing.
That 10 looks nice, but I would stick to looking for a Suburban, preferably a SS model with twin Onan....I've got 5 in my stable right now!