To rephrase the basics:
Problem: Large amount of small clans which are often abandoned and take-up the names and clantags.
Proposed solutions:
a) change the required members for clan (from original 5)
b) introduce lvl requirement for creating clans
c) propose some way to regain names and clantags from inactive clans
I think we may need 2 or even 3 of those, actually. Firstly:
a) 5 members is awkward as hell, but then again I think 8 is too many. Either back it down to 4 and embrace the clan swarm (about that in a moment) or I say raise it up to 6 because it's less awkward than 5, it's two ships with almost-full crew or one full ship and captain+one crewmember. Both of those options are equally valid for me.
b) Level requirement is scary as hell for some people, but it can be as low as, I dunno, 5. I think some symbolic compromise would be that non-novice players can join clans, but they can't create them. For novice time (like, what, 10 hours of gameplay?) they'd have to manage with friendlist and party capabilities.
Edit: What if we did a cruel joke and only let people make clans after they have finished tutorial?
Mwahahaha// Personal note - I think there is something in keeping the clanlist clean, because I know I joined a mostly inactive clan once and felt weird. Literally for a week I was the only guy online.
c) As someone suggested, just [If clan has less than {minimum required} members for 3 (or 6 perhaps?) months - disband that clan] thing. But what if clan has members but all of them are inactive? Huh, I guess some percentage of activity requirement? Like if for X amount of time less than Y% of people logged in then disband clan? More humane would be to just put a warning first. Throw in your ideas, but I think this is the best thing we can do.
Also, clan has some capabilities that have effect on gameplay. This is like friendlist-PRO, becuase you can set some kind of rules and restrictions for joining your clan and form for instance a band of 1000+ matches vets who crewform together, which is op in pubs. But unlike friendlist you don't have to know all those people, every clan member once in a while adds someone and that person serves as a friend-PRO for all the clan.