You really don't have anything to do to get to the best ending. You really just need to get enough money to travel between towns, then you always have an option to get to the wedding and object . It really doesn't matter how much you gain.

You can obtain all the figurines or not, you can sell the guitar or not, the fishing rod (ok, just be sure you have enough fish to get to the end though, because my character died of starvation one night just because I made her go to bed without dinner, for ONCE) - it really doesn't matter, just be mindful of your dialogue choices and that's all. I've been following a guide for a while because I thought I had to become rich in order to get to the wedding, buy the dress and all, then I got tired of fighting at the gym... and it really didn't change a thing. I got the "good" ending and I got all the achievements, 100% complete.