1. The helmet is fine. Snell's SA rating means "Special Application," while their M rating simply means "Motorcycle." The SA rating adds fire resistance to the tests the helmet is subjected to and passes. That said, Snell rating has nothing to do with the legality of the helmet. For that you want the DOT sticker at the base of the back of the helmet. The DOT sticker is on the outside of the helmet, and the Snell sticker (if it has one) is inside.
2. If the jacket fits and doesn't have any stitching missing or anything then it's probably OK. You want more than a jacket, though.
Boots that are at least over the ankle. Normal shoes easily come off if you're sliding down the road, or get snagged on the bike during a fall and get torn off. Also, nothing sucks like putting your foot down at a stop and having the shoelace catch on the peg or something.... Most motorcycle boots have ankle armor, as well, and a lot of them are waterproof.
You need gloves to protect your hands. Not those stupid fingerless gloves the Harley guys wear. You can get shortie gloves that don't go over the jacket sleeve, or gaunlet gloves that are longer. Fitting gloves correctly is about the hardest part of gearing up, though. One type will fit your hand but the fingers will be an inch too long. Another type has the right fingers but the hand is so loose the glove would slide right off in an incident, making it worthless. What you want in a glove, though, is hard knuckle impact protection and durable abrasion resistance in the palm.
Pants. What, you thing your ass doesn't hit the street if you go down on the bike? Why U No protect your legs? OK, it's a hassle to change clothes to ride, wearing riding pants to work, then changing to your work clothes. That's why I wear overpants. Protective motorcycle gear that goes on over my regular street pants. I have abrasion protection, hard armor at the knees, and padding at the sides of the hips. But don't think that jeans give you good protection from road rash.
You've got a jacket, and Tour Master is a good brand. What you want in a jacket is impact protections at the elbows, shoulders, and spine, and abrasion resistance everywhere. Jacket and pants should have a way of zipping together, too, to prevent the jacket riding up or the pants coming off during pavement surfing.
Helmet should be full-face, no question. More than half of head impacts in a motorcycle fall are to the face and chin area. I personally can still speak clearly and chew my own food because I was wearing a full-face helmet when I needed it. Snell-rated is a higher test standard than DOT, but DOT is what you need to have a legal protective helmet. A lot of guys like the modular helmets where the whole front section opens up so you can get a snack or a drink without removing the helmet; the convenience of open face with the protection of full face. And don't ride with the visor up. I see that a lot, especially if it's hot, but taking a bug through the visor opening at 70 mph will not be a Good Thing!
As to type of gear, leather offers the best abrasion protection by far. One-piece leathers can't come apart the way jacket-and-pants might. But two-piece leathers properly fastened to each other is just as good on the street (but not racing, or track days.) Leather is warm, though, if you ride in the heat. You can get textile gear, and mesh, as well. Mesh is great because air passes right through it, yet it offers good protection from road rash. I wear mesh, being a Florida rider and often seeing 95+ days. My mesh jacket has leather on the impact areas for best sliding protection and still being breathable.
3. Costs - 70mpg might be valid for a 250 or a small scooter, but you'll probably be more in the 50s. I get in the 40s on the highway with my FJR 1300.
Motorcycle tires are expensive, costing as much or more than car tires, and they don't last as long. A lot of bikes won't get 10,000 miles on a rear tire, and you could easily drop 200 bucks every time you need a new one. Fronts usually last longer as far as tread life is concerned, but may actually need replacement before you wear it all the way down because they cup, or waer grooves off the center, causing them to behave poorly when tipping in for turns, or maybe causing front-end wobble. Proper inflation is vital to tire life.
Bike maintenance. You change the oil more often on a bike than you do a car, because the engine oil is also the gear oil in the transmission. Count on an oil change at 3,000 miles, not the 5 or even 10 you'd get with a car. Valves on most motorcycle engines do not use hydraulic lifters, so they must be periodically checked and adjusted for clearance from the cam lobes. Adjustment is usually by changing shims in the lifters, which requires removing the camshafts, so valve checks will run a few hundred dollars at a shop, mostly for labor. It's something you can do yourself, but have someone take you through the first one or two jobs.
4. Being that big (and I know what of I speak here!) you don't want a bike that requires a tank-hugging, leaned-over riding position. You want to be close to upright, and you want your feet under you, not way out in front like cruisers. That foot-forward position puts weight in the saddle on your tailbone, which will be excrutiating after a few miles. Most cruisers need a good stretch to reach the bars, too. Why, I don't know. I guess they think sitting 5 feet behind the bars makes you look cool. It's stupid and seriously fatiguing. probably one of the reasons most cruisers only carry around a hundred miles of gas. Who wants to be on one any longer than that?
A dual-purpose bike will have a good riding position, as will most of the "starter" bikes out there, like a Suzuki GS-500. (If you can find one of those, get it. Best starter bike in the Universe!)
I don't know of CA requires an MSF Basic Rider Course to get a motorcycle endoresement on your license, but take it anyway, even if it's not required. You do NOT know how to ride a motorcycle, and Youtube is slam full of videos of guys being "taught" to ride by friends. Your friends can't teach you how to ride. Telling you there's the clutch, there's the brake, there's the gas, let's go doesn't come close to cutting it! Take the damn course and save your life. or at least your bones!