Rex' scavenger rank resets. Similar logic as with Ursula's quest applies. If you are close to the highest rank, you might as well go for it to obtain all rewards from rank ups.
If you haven't completed town development yet, use your money to get it done. Spending money in shops is the quickest way to raise the development level. There are numerous perks that come with shop ownership that are notably beneficial, especially if you reset all characters' level to 1 on a new game+.
There really isn't much that has to be done as preparation. Resources like money and core crystals - which you could gain by opening all treasure chests in the game - can be easily built up on an already started new game+.