Hi, welcome to TamaTalk!
Answers:
1. Try posting in the "want to buy" section on tbay. Try looking in the "want to sell" section to see if there are any people selling them already. Also look for them used on ebay.
2. The V4.5 has 5 games once it's a teen, then you can choose another one for the Tamagotchi's job when it becomes an adult. A Tama-Go comes with two games installed, plus a "lite" figurine with one game on it. Buying more figures for the Tama-Go gives you access to exclusive stores and games. But on its own, the V4.5 has more features, such as work, items, and souvenirs. AND a TamaTown that works if you use the Europe version.
3. Yup, it's normal for "lite" figures (the ones that come with the Tama-Go) to only have one game. To expand your selection, you'll have to buy figures separately. Each of the separately sold figures has two games and one shop.
Also, please note that the Tama-Go is much easier to care for than the V4.5 is. Tama-Gos can't actually die!

If you see a Tama-Go available for $3, you should buy it, they'll be rare collector items in a few years. You might also see Tama-Go figures at that store for pretty cheap. It would be prudent to buy those as well.
Good luck with your Tamagotchis!
Hope this helped!
~Amat