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Just wanted to know how frequent do you all do water changes, and if it's partial or complete.

I do partial water change once a week (about a third), and do a full water change only if the water becomes cloudy/dirty for some reason. I also add bacteria to the water every two weeks.
If I do a full water change I also clean the filters and everything in the tank. I just upgraded to a 55 gallons so I don't know how long this one will hold up but I expect the new filter to keep the water pristine for at least 2 months if not more. Pray for me.

I wouldn't add anything when you do water changes. As for frequency, I'd do what's convenient, and your partial water change is good... maybe once or twice a month. Depends on how strict you are about your water parameters. The water may look clear, but may not necessarily be clean.

I usually let evaporation do the water changes for me. The water evaporates at about a rate of 5-10 gallons every 2 weeks for me. I keep my 50 gallon stock tank 75% full. That's about a 25% water change that happens on its own for me. I do have a good water flow though, a larger than normal surface area (stock tank) and a bubbler (for the fish), so I imagine that all aids in speeding up the evaporation. The filter is packed with Seachem Matrix too; all it has is Seachem Matrix and some foam mechanical filtering pads. It's a filter rated for 100 gallons, and it keeps my 50 gallon stock tank running well. All of this keeps the water crystal clear, with very good water parameters. From what I've found, if your filter flow is good (have the output setup on one end of the tank and input on the other side), and you have enough turnover of the water (in the form of a 2-4 times the gallons per hour of your tank), with plenty of good filter media, you'll have good water.

Remember when cleaning out the filters and the tank to not get rid of all of that brown, nasty looking stuff you might find in the filter and in your tank - that stuff is gold. It's full of good bacteria, and only needs to be cleaned if it is restricting flow. Clean that stuff in tank water, and be gentle. You don't want to kill off too much of that bacteria, or else every time you replace that good bacteria with a fresh pad or filter media will mean starting the tank cycle all over again. If the filter media starts to deteriorate, and you want to replace it, you want to "condition" any new filter media you are going to use before completely removing the old media. Place the new media in with the old for several weeks, and let the new stuff grow bacteria from the old stuff.

Of course, the only way of knowing whether your water parameters are good is by doing a full chemical check of the water. Otherwise, a visual inspection is usually a good indicator if you are on the right track.

Everything is noted !

It's currently winter so evaporation isn't really something that happens a lot, but in summer DEFINITELY ! I need to put an iced bottle twice a day for the water to be at the right temperature.

It's still good to do a partial change... there is waste in the water that doesn't evaporate, and just topping off the water will increase water hardness and concentrate that waste. What kind of filter do you have? If you have a canister filter, make sure you have bio media as it will colonize that good bacteria rambologic mentions. Some people with big tanks just have a separate filter filled with bio media.

I'm not planning on stopping my water changes if this was for me ahah