Bel,
First off, what park, what day. Since you are not staying on property, you want to avoid the morning and evening Extra Magic Hours. That way you avoid the bigger crowds. So here is where I would go;
- January 7 - Magic Kingdom
- January 8 - Epcot
- January 9 - Animal Kingdom
- January 10 - Hollywood Studios
As for tickets, buying in advance is not going to save you a ton of money, unless you are able to buy them via a reputable ticket re-seller, like AAA. But know what the prices are before you go, so that you know if you are getting the best deal at your resort. If not, buy them at the gate, so that you are sure you are getting valid, well priced tickets.
Most shows neither require, nor have, reservations. That, of course, does not include dinner shows, which do require them. But shows in the parks, don't need them. So you should be fine.
Your question cut off after that, but it looked as if you were saying it was your first visit? So let's do this. Write me back with any other questions you have, and I can help you get yourselves squared away!
Have a magical vacation!