I could go either way when it comes to a four or five. To be honest, my Carvin does the five string Jazz thing perfectly for my taste. It gets that ash body, Seventies tone as good as any Fender in passive mode, and it is a cracking good active Jazz to boot. The Nash would be killer Sixties style bass. Maybe a four would be better if Nash uses the U profile for a five like they do for fours. That U profile is chunkier. It is cool on a four, but it might like a Warwick on a five. I can play Warwick’s just fine, but it would seem odd on a Jazz.
My thing about relicing is that often it just looks fake to me. I would just as soon buy a new bass that looks new. Finishing the neck to give it used feel, however, is a great idea since it makes the bass more playable.