What you do in character creation doesn't really matter. The only difference between starting characters is their equipment (spellcasters have an advantage that can last a while). You'll be able to smooth over the difference in stats very quickly.
For a fast, finesse-centric (not stealth! There are only a few opportunities to sneak up on or past enemies in the game, although there may be some magical aid hidden somewhere) character, get some form of short sword, dagger or rapier/foil for your main hand and a parrying dagger or buckler for off-hand. Basically, give each new weapon you find a few test swings to see which feel best to you. Light weapons tend to scale with Dexterity, so invest in that.
Use light armour and keep your equipment load low. You get a mild penalty to your rolling speed at 25% maximum weight, and a heavy one (that makes rolling A Very Bad Idea) at 50%.
Keep in mind that even though such methods are quick by Dark Souls' standards, the game in general still has relatively slow and methodical combat, so expect to fight defensively, keep your distance and try to parry blows a lot. Also, don't ignore other weapons entirely. A long stick and a heavy shield can make certain areas a great deal easier, even if they aren't your best weapons.