That's a wonderful idea! Good of you go get involved
The best place to get people interested here is probably ingame though; because here on the forums the majority of players are well experienced already and would easily exceed the Level 5 rule. There'd need to be promotion ingame and on Steam probably to catch people who haven't played that much or not cared about getting their Achievements higher.
As you've maybe seen on the other Tournaments, it's often a problem to even just get a full ship with 4 players - Maybe beeing more loose here and allowing AI Crew, or restricting the ships to Pilot, Engineer, Gunner + 1 AI Engineer could do the trick here to get the required number of players.
And, the longer the Tournament takes the more difficult it will be - even with the above rule - to keep all the players aboard. Consider that less experienced players are less likely to stay with the tournament and crew for so long because they might not be so well connected with each other yet.
For this kind of Tournament I'd even suggest a ship based approach.. Captain's sign up their ship and replacement pilots, and at the end there's checked which ship won the most matches and which people served aboard that ship. Might be a bit of a hassle to write it all down, but screenshots at the matches ends should suffice.