1,2,3 you can all find out with a quick search and a couple of youtube vids. If you do not have lube then take that into account when buying, but there are people that will lube switches for a cost but will be worth it if you get it from the right person. Cobert from the mgb discord is a good example.
4. All keyboards will sound different. you can make it sound different with mods and many different factors. Watch nearLucids "Why keyboard sound tests are lies" vid for more details. A very prominent mod for "newbies" is the pe foam mod, it makes a very nice sound but gets rid of any character a keyboard has, but unless you want to have diversity in your sounds, it is still a very good mod.
5. bottoming out is not necessarily a bad thing, it is all preference, if you do not have the money to buy multiple switches and experiment, then simply get tactiles with springs greater than 50g. Spring swaps are a thing too, so if you do decide to go with expensive holy panda clones, then they will not be wasted, but linears are not a bad option too, and there are many cheap options for those, check youtube again for good ones.