what would happen if a NT manager doesn't arrange a friendly match or doesn't find somebody free to arrange ?
Well, I guess the NT would not play that week. However,
NT managers shouldn't have any trouble finding at least a small NT without a manager to play since there are more nations without managers than with, surely. A NT manager unable to find an active NT to play, and running low on time, could still arrange a match
instantly by selecting one of them (ideally from an easy to access list of available NTs for the given gameweek).
Arranging a friendly should be SO easy that failing to arrange a match for two or more consecutive weeks might constitute grounds for removal of a NT manager. By allowing matches to be scheduled in advance (rather than just week to week like club friendlies) this shouldn't be a problem for anyone. In fact, a manager not wanting to spend much time on it could simply go through and arrange matches for the entire season with NTs without managers in under 30 minutes and be done with it. Or, they could spend some time arranging matches with active managers and joining custom cups. I'm sure voters would prefer the latter.
Additionally, there is also the issue of what to do with prize money from custom NT cups. Eventually I'd like to see NT have ways to spend money, such as on a National academy, NT physio, as well as coaches and other facilities that would improve training bonus from NT matches. Part of the prize money could be distributed among clubs that have contributed to the NT account over prior season until such NT features are developed.