Hello RPMini
Welcome to the infected!!
Since your still looking,
1. Take the MSF beginner training as soon as you can.
2. Get your M1
A. What is your inseam length? 32 inches or more your golden with any Vespa. 29 to 31 you can still ride but it will be trickier.
B. Pick out your scoot
C. Find her and bring her home
D. Get Insurance
You can do these in any order, but take the MSF then get your M1 - much easier and cheaper.
check out the schedule for the MSF (Motorcycle Safety Foundation) course nearest you, then get signed up and take it as soon as you can. They may be booked up for a month or more. It is about $250 for the beginner course. With it you will get a discount on your insurance, will not have to take the DMV riding test (much harder to pass than the MSF)
Once you get a scoot, before or after the course, get the feel of the scoot. Take it very slowly. sit on her while she is off the center stand and plant both feet if you can, and lean her a little both sides, feel how heavy she gets, even with a little lean. Have a strong friend on hand if you really want to push it.
Then take the scoot out for a ride around the area, stay on streets or parking lots (empty if you can find one), remember most people drop the cycle or scoot when going less than 20mph. Do not turn on a greasy spot in a parking lot. Practice low speed maneuvers, you can download a few documents here, I think they are in the wiki. I just looked and can't find the one that shows the layout for the slow speed maneuvers. But here are some good links to answers:
https://modernvespa.com/forum/wiki-new-owner
https://modernvespa.com/forum/wiki-safety
Some info to help learn more about scoots in general:
https://modernvespa.com/forum/wiki-publications
As for the scoot size, either the 250 or newer 300 will work well for any riding you do. Just because you have a short commute doesn't mean you have to take the shortest route!!

You may only plan on riding short commute stuff for now, at some point your going to want to ride it more. Find a local scooter club (biased for the Royal Bastards myself) join them for some rides and meet-ups, it is a great way to see different scooters and hear great stories, and meet good people.
Your eyes will dry out too fast without some type of face shield or goggles, so the helmet style is your choice. Try on as many styles and brands as you can till you find what fits your head. A Nolan N102 fits me very well, but may not feel good for you. Helmet types are 1. Scull cap (above your ears), 2. 3/4 helmet (covers ears) 3. Modular (has flip up chin bar) and 4. full face (integrated chin bar) I think the modular is the best of both worlds, as I can flip it up at stops to talk, eat, or whatever. It gives me chin protection (most likely to hit the pavement in a bad crash) A helmet is not much use until you crash, then your going to want one.
Problem is you will never know when your going to crash. If your claustrophobic, you will not want a modular or a full face, but might be able to wear a 3/4 with a flip up face shield. The options are very many, and it will be a hard decision, but you have to make it for yourself.
So for now research research!! find out what helmet you like, and or can live with. See what scoots are available, there are lots of styles out the The Vespas sit tall, and have 10 to 12inch tires, but have the uni-body metal frame, and classic scoot style. There are a lot of scoots with up to 16inch wheels, which give a smoother ride, so are just as nimble as a small tire scoot. Power ranges from 50cc up to 650cc, Vespas stop at the 274cc GTS300 super. You have to go to the Maxi style scoot to get a 450 to 650 scoot. Then there is the MP3 three wheeled scoots. So lots of choices!! have fun!!