I love playing weak characters
Ah! Then disregard my previous comments. In multiclassing Wiz/Sor, you have pretty much made the best selection in all of Dungeons and Dragons if this is your goal. Hmm...the problem with almost everyone else's advice (like Practiced Spellcaster) is that it is going to make you unhappy in the end. Why? Because Practiced Spellcaster is going to make your spells do more damage, and increase your caster level, making you unhappy.
Your best bet is probably to follow Particle Man's advice and multiclass into both psion and wilder, ensuring that you never have to deal with high level spells.
As for feats, the Player's Handbook has some real gems that you should take. I suggest taking Alertness as soon as possible, since it is unlikely to make your character too powerful for your liking, since you already have that ability whenever your familiar is around. Also, Deft Hands is a good choice. Any of the +2/+2 skill feats would also be good, except Magical Aptitude, and Skill Focus in cross-class skills also shouldn't be a problem for you. To emphasise your dark nature, get Deceitful, and then buy cross-class ranks in Bluff and Intimidate.
As for spells, Animate Rope won't disappoint you by being too powerful. Unfortunately, many of the other 1st-level spells can be annoyingly strong in many situations, but fortunately, the 2nd-level spells include such useful sundries as Leomund's Trap, which won't be too powerful unless your DM throws lots of NPC thieves against you who try to steal your possessions.
Speaking of possessions, Ring of Clumsiness, with its 20% spell failure, might help if you are getting off your spells too often. Of course, its cheaper to just wear Chain Shirt to get the same spell failure, and it shouldn't make you any stronger than a normal Mage Armour.
Random tangential question: Is Spanish your first language? I ask because using "anybody" in place of "nobody" seems to be common among Spanish friends of mine, and I saw you use the same idiom.