When i create a brush with nodraw and make it hollow, then i texture the inside and start working from there on my jumps. But then i sometimes get entities randomly leaking straight through walls which i can fix by simply texturing the entire brush ( so also the outsides that are never seen by the players). Is there anyways to prevent this from happening while still being able to use nodraw as much as possible?
I'll leave it to someone else to fix this for you, but you shouldn't use hollowed out brushes. Afterglow's tutorial lies. It's just easier to mold later if your jump needs to be stretched or just changed around in general. When trying to move around a hollow brush it can go off grid which is always annoying.
hollowed out brushes are fine, where are you getting your information from? using the carve tool, however, is not a good option
my maps aren't optimized for the most part and some of them took 30 minutes to compile. you NEED func_detail on ramps (especially curved ramps) or else your compile time will shoot up towards 1 hour or more.
nodraw on sides the players can't see are also very useful in lowering compile time (and with curved ramps, will remove most of the zero child area patch errors). func_detailing smaller brushes is generally a good way to go and there's no harm in doing so.
lightmap optimization will save you vrad compile time as well, because if everything is at 8 or 16, it's going to be a while, but if everything is at 32, then your map looks kinda bad with the shadows being blocky. This isn't as important but if you want to make your map look good and not have to wait hours, then do this as well.
on topic: nodraw on the outside should be fine. water textures and any brush entity or displacement will not seal off the map.