Thanks. 4th level, and I'd like to choose my race from those in the SRD.
I'm leaning towards human, halfling, or gnome.
28 point buy.
I don't know if you already picked your spells or not, but I'd suggest:
Level 2: Glitterdust
Level 1: Enlarge Person, Grease, and Charm Person.
This gets you a solid combat buff for your melee allies, and you have some pretty good crowd control targeting tow saves. Charm Person can be good in and out of combat. Consider picking
Alter Self for your next 2nd level spell. It's good out of combat but it is a solid combat buff (+6 natural AC as a troglodyte).
Mage Armor might be attractive at this level, but you might want to check with your DM about the availability of magical items. A
+1 Twilight Mithril Shirt (Twilight is in Book of Exalted Deeds/Magic Item Compendium, Mithril is in DMG) can get you +5 AC with 0% arcane spell failure. You can wear it without proficiency (-0 armor check penalty). If this is unattainable, you might want to swap Grease or Charm Person for Mage Armor.
Human is likely your best race, because of the bonus feat. Halfling and gnome are okay, but your speed will drop down to 20'. You could overcome that with a riding dog, but that opens up other things to worry about.
As far as feats go, it depends on what you want to focus on. Getting a couple metamagic feats isn't a bad idea to make your spells better. When focusing on crowd control, I like Extend Spell and Sculpt Spell (Complete Arcane). They can give you new AoEs to work with and also help you sculpt your spells in ways to avoid your allies. As you gain levels, if you start picking up some blasting spells, Empower Spell can be handy. Maximize is pretty overpriced unless you can get some metamagic reducers.
If you ever find yourself with a spare feat, Improved Initiative is always good. If you focus on Conjuration-based crowd control, Spell Focus (Conjuration) and Greater Spell Focus (Conjuration) could be worth the investment. If you go this route and also find summoning an attractive option, Spell Focus (Conjuration) gets you the prereq you need for Augment Summoning.
As far as tactics go, figure most of the time, you will be staying back (out of melee) and just using a crossbow (or similar weapon). You will use your spells as needed, but probably not every round. If cast early (or before combat), Enlarge Person will give a solid boost to damage for the entire fight. The reach granted from being large-sized can give your ally first-strike, and this will save HP, on average. Glitterdust can
blind* several targets 140 feet away from you. This is four rounds they can't do much of anything useful. Grease can hold people in their location for a round or two.
* In addition to everything listed in that link, a blinded person cannot even target you if they don't know which square you're in. If you move out of your square afterward, they only ways they can find you (apart from guessing) is with blindsight (most things don't have that), scent (if they're adjacent to you), or by beating your Move Silently check with their
Listen check by 20 points. So, even taking the -5 penalty to Move Silently for moving at full speed, you're still 15 points ahead of the guy on his d20 check to find you. Remind your DM of these rules if the monsters always seem to "find" you guys.