How many spells are there? Which is the best? Is that to keep the TV under control? Fourteen providing enough spare bodies to last the game. Does the number of the players on your roster depend on the squishiness of the team? Would a Skaven team keep more players on hand than a Chaos, Tomb King or Dwarf team? What about a team like Snotlings, would they roster more players in order to have sufficient replacement players to make use of their swarming rule?
I would keep it to 14 so you can induce up to 2 star players. Especially snotlings. Once you're at 16 you can take no more players (with the exception of riotous rookies), even star players.
This is in addition, meaning you can have up to three apothecaries available to you over the course of the game if you also take the ordinary one. Whichever you feel is more pressing. My group tends to view journeymen as convenient scrimmage fodder or fall guys for fouls, and we don't tend to play with star players anyway, so for us it's a no-brainer to include them if we have the inducement cash left over to do so, be it when we don't have a full roster or have people missing that game. There's also the fact that, especially when a league is starting, you won't have sufficient difference in TV between teams to be able to afford star players as inducements. It's also been my experience that, by the time there is such a gap, the other team is likely already leagues ahead of you in its ability to win games to the point where you having a star player or two won't really matter in the grand scheme of things.