My current RotRL campaign has:
human Paladin- tank build
human Fighter- two handed fighter build
half elf Arcane Archer
half elf Mystic Theurge
Two of the characters have cohorts, bringing another healer and another archer. Overall, I find the group is light on magic. A straight Wizard would be excellent, or at least a Sorcerer.
It looks to me that your group will suffer in the same way, since you have only a Magus as a caster. While the Magus will have plenty of combat spells, the broad utility that a Wizard has will be missed. You could make up the difference with another limited caster - a Bard, for instance. Or a Sorcerer who carries plenty of scrolls and wands could probably do the trick.
As a side note, I'd advise you to impress upon everyone the usefulness of ranged combat. Everyone should (unless the unarmed Monk is prohibited) have a missile weapon handy, especially if you have no dedicated archer.