1. Make sure to be constantly checking his/her hearts to make sure that they're not hungry, stressed, or unhappy. Play lots of games with it, it makes them happy and skilled. Pause it when you can't look after it. Also, tamagotchis wake up really early. So, if you're not awake at 7am-8am, bad things could happen to your tama. Don't worry though, this can fixed. You can adjust your tamagotchi's time so that it wakes up at the same time as you do.
Example: you wake up at 11am everyday, but tama likes to wake up at 7am. What you have to do is set the tamagotchi's time 3 hours behind you so that it thinks that 11am is 7am.
Also, not sure if all newer versions are the same (V6 is the only new Tama I've played with). But with V6 (Music Star), the only food that you get is 'Baby Food' When your tama becomes a teenager, baby food does not satisfy its hunger. So, you have to use all the money that you get from the tama king on food, DON'T WASTE IT ON ANYTHING ELSE! and try to buy cheap food items.
2. They sell Tamas at Walmart, Toys R Us, etc for like 16 dollars or so. You can also buy them Online where they're usually cheaper (be careful though, lots of online stores sell fakes.) I personally bought mine at Ross, it was brand new, original, and it only costed me $4.99.
3. My very first Tamagotchi was the P1, I think that was back in 1996? idk. After that one ran out of batteries, I didn't have a tamagotchi for a while. Then, during 8th grade (2004) I had two more Tamagotchis... can't remember which version, it was either v1 or v2. I don't know, maybe it was another version. Then, I got myself two V6's (a friend from university took one of them. So, now I have only 1) Right now I'm in the process of buying a P1 Tama (same color as the one that I had when I was little.),and Angelgotchi, and a V5. I WANT TO COLLECT THEM D: