Well, you don't need Rogue to enter the class... the requirements are:
Any evil alignment; sneak attack +1d6; Hide 6 ranks, Intimidate 4 ranks, Knowledge (local Waterdeep) 3 ranks, Move Silently 6 ranks, Spot 8 ranks; Great Fortitude, Iron Will.
So... 27 skillpoints, min level 5 due to 8 ranks in spot. Meaning any class that grants 4 Skill points per level will give you 32 by level 5 and be more than enough. 3 skill points wouldn't be enough... so any class with +2 int, or a 4+ skillpoint per level with +0 int is enough.
Great Fort + Iron Will - you can get these from domains... but being a spellcaster is a massive waste for this class. I guess you're burning 2 feats, human/strongheart halfling gives you a spare feat, if not your lvl 1 and 3 are taken by this feat tax.
Sneak attack +1d6 - you can get this from an item... like an Assassination weapon.. but thats 8000 gold... and is wasteful unless you have a death attack... unlikely.
Similarly Bracers of the Hunter grant +1d6 SA and cost 8,500 but are better because they also grant +2 initiative and +5 to hide checks.
or for 8,000gp Mantle of the Predator - 1d6 SA and +5 to hide and move silently.
There might be a cheaper way... at lvl 5 your WBL is only 9000... so this is possibly too much... with the weapon route you can obviously build that over time... start with a masterwork, enchant to a +1, enchant to a +2. The items cost 50% to craft along with XP...as an option... or your DM might grant you a special quest or some malarky for a specific item... or you could just find a cheaper one.
Evil alignment... well.... that's easy.
I've always liked Monk 2 combined with Ninja, decent Wis and Cha synergy, with lots and lots of invisibility, very flavourful as well by being a Ninja with monk weapons... also solves the sneak attack expense problem.
I like the spellthief idea but not sure how you'd build it.
