Upgrading To A Larger Fish Tank?

Alright, here’s the deal. I have a small 10g tank right now with about 5 – 7 Sword tails and an algae eater. I really want to upgrade to a larger fish tank, somewhere within the range of 55g – 75g. I’m thinking about a 60g tank. What all do I need to do for this new fish tank? I understand most of the basics already, seeing as I’ve kept fish before. On another note- this larger fish tank may become an additional tank, and I’ll give some of my sword tails away. If I do this, which would be easier and more rewarding: either having a freshwater tank, or saltwater? I have absolute no experience with saltwater aquariums, but the fish you can have just look gorgeous!
Are there any beautiful, gentle-nature freshwater fish that are not that expensive? I’d hate to spend a lot of money on this. I know these are a lot of questions, but please bear with me. If this *isn’t* an additional tank, should I move over the gravel from my old tank to the new one, as well as buy more? Or should I do a substrate flooring instead? I plan to have many plants in this new aquarium. I don’t want to have sand, as I’ve heard it can mess up with the filter.
Speaking of filter, would I place the old one in the new tank or buy a new one? Because frankly, I’m not happy with my filter at the moment. My algae eater got stuck where the water flows out last night. My dad and I had to pour all the water into the fish tank to get the poor guy out. I’m afraid something like this may happen again. It gave me a very bad scare. Is there any types of filters that are somewhere near 100% safe from things like these?
Once again, I apologize for all the questions and in a messy order. I’m kind of just thinking and typing my thoughts at the same time, LOL. On the other note, I noticed some of my sword tail fry have been disappearing. Well, they are not really “fry” anymore, per say. They are halfway grown adults. I’m also worried about the father of these fish, he doesn’t move around much. He just rests at the top of the fish tank and, well, hovers. I have air pumps and such so I know it’s not that he isn’t getting enough oxygen in the water. And quick question, (well a lot more of them, anyway.) what exactly *is* a water change? I mean, I add more water when it evaporates from the tank, (which happens quite often,) but what is *really* a water change? Sorry for these silly questions, it’s just that I’ve had this fish tank for a long time and I never really learned what it is.
Thank you for continuing to read this and answering! I really appreciate it!