Welcome sheiky. Hope you find all the info you are looking for here. I'm still pretty new to the forums myself and still looking around through the thousands and thousands of posts on here, lol
I agree with the other posters here. Focus less on the number of domains you want to own, and more about what either the purpose for each domain is, and/or research what the potential sales value may be for the domain(s).
If you happen to have a business, for instance, focus more on getting the domains that will target the services you offer, and ones that you know your customers are keyword searching for. For those types of domains, YOU will know the value of them because they hold value to you and your business.
For everything else... a lot of it is "eye of the beholder" regarding value. You may have something that surely must be worth something, but there may only be one other person out there who had a similar idea and decides they really want your domain. Just because some other domain sold for 100k doesn't mean that every other domain like it will. Every so often though, you may wind up with a domain that a lot of people want... then, you've got a good one most likely.
Remember, domaining is very much like gambling. Each time you spin the slots you may think it's going to give you the winning hand.... but very rarely will it. There will be good days and bad days, and bad domains and possibly a great one every so often. Just be prepared to invest with little return, and some domains you may need to be patient with and wait for the right moments to try to do anything with due to trends, etc. Then again, there will be some domains that are simply duds from the get go.
I am in no way an expert at doing any of this, but I've done it off and on over the last 10-12 years or so. I own a bit over 200 domains... but 80-100 are specifically related to my own business, etc... so about half of my "investment" are keepers for me. Since those domains hold value to me and/or my businesses direction - it makes sense to continue paying for them and protecting them. The other domains... well, some I feel are worth something, some may do a whole bunch of nothing. Who knows. But it's also part of the fun of doing it is to see what happens.
But I will note, for me - I always look at it that if I "invest" $10-20 on a domain... and if I'm able to make anything over that - then it's profit. It's always better to accept anything that to just drop the domain, because then you get nothing back from it at all.
Just my random thoughts. Good luck to you!