I highly suggest you do some reading. Lots of factors to take into consideration. If you're doing a dedicated panel to your aquarium setup, you need to take into consideration things like distance from your main box, how much draw you've got on it, I would suggest going ahead and spending the extra on GFI breakers vs GFI outlets since you're dealing with water.
Things like, do you have a crawlspace, or are you running it up into an attic, then fishing it down into the walls all have consideration. If you may sell anytime soon, you may want to seriously consider a contractor so it's done to code.(not saying you can't do it yourself to code, but a contractor will know what permits to pull, and get it inspected so there is no concerns for the new buyer)
Otherwise adding a panel is easy. It's a matter of adding a line to your main box outside, then running the appropriate sized wire for the load to the new box location. Calculate your peak amp load, then add at least 50% for a safety buffer*. I would suggest doubling it.) running the cable into the box, then adding the breaker to the bus and running cable to your outlets/appliances. Biggest thing is making sure the wires can support the load without overheating and becoming a fire risk (THIS IS A VERY REAL ISSUE!!!!!!!) DO NOT OVER LOOK IT! ESPECIALLY if you're running it through your attic or crawlspace. if it overheats and starts to melt, you won't know till it creates fire. You can't go too big, but to small a wire and it will just burn through and short, and you'll be hating life trying to find the short. Just because it melts through, doesn't mean it will melt through the sheathing on the wire.
Use extreme caution playing inside your main box, invest in a voltage ticker (little device that you can hold up to a wire and it will tick if there is current on it). Don't assume a line is a dead line until you've put a volt meter to it, and can confirm it's not carrying current. Having had the experience of touching a live 220 line, and 120 line I can say, 120 is uncomfortable and will make you jump. 220 put me on my knees and made me want to cry like a baby. (working on a homeowners place that put a screw through a 220 line and didn't know it. when I put an uninsulated screwdriver on it to remove the screw, well yeah, I wasn't a happy camper)
My BIL actually still works as an electrician for a living, (I did satellite work and had to do light electrical work due to my job) and ended up with an overnight hospital stay when someone threw the breaker on a 3 phase line he was working on, thankfully he was pulling his hand away when it powered up, and it only arced to him vs him actually having a grip on it. Point is, don't underestimate electricity. It's one of those things that will make you hate life if you're stupid with it.
My experience is as I said, light electrical during satellite installs. Fixing circuits in an old house, in ground pump well work, wiring up a 36x30 shop, some AC
work, and building wiring harness's for race cars. Good luck with it.
* you can go with less or more as a safety buffer, it also allows you to add more to the circuit later down the road if you go with more load. Easy to add when your first installing, can be a pain, and cause issues down the line if you don't take it into consideration.