Unless you want XP penalties, you wanna go Illusionist. If you go Illusionist you definitly want Spell Focus, and maybe Greater Spell Focus. This is almost a requirement for Illusions because of the double save. Illusions are quite powerfull, but the double save is a big weakness.
Rogue is a great choice because you can have different class levels in rogue and not take an XP hit. The DEX bonus is nice too. If you wanna play any other kind of mage than Illusionist, pick Halfling.
Spellcasting Prodigy. Bah, its good but not broken. The 'must take at first level' has stopped me from building a killer early-game combo many times. Its allowed in my group, one caster out of 3 or 4 has taken it. If you are gonna be an Illusionist though take it. You need every point added to saves you can get.
EDIT: The being small part of a Halfling is a very cool thing. The elf gets auto-search, which is nice but no big deal since party's go search-crazy anyway. Lack of movement is bad for the first few levels, but get some boots of Striding then give them away when you get Fly. A hafling Rogue can use a short bow, who cares that an elf does 1 point more damage? Drop a Fireball, NOONE cares. The best part of being small is that everyone else is so big. Sit in back, look innoculous and you will rarely be targeted. If the enemy gets smart and sends his archers after you, heh, good luck hitting a 3' skinny hafling hiding behind 300 lbs of armored half-orc. Oh, and for more mobility drop 5 points in Ride and take a riding dog.