depending on your level, i normally have around 30 - 40 dex, rest is on agi, str not so much cause a high atk dagger should do the trick (damascus is a goody) I've build tons of thief classes so i can relate to your situation

and apart from that when i started playing on this server which was years and years ago, i started out as a thief
What i did was lvl a novice to 30 with the novice gears purchaseable in the novice shop, just go pyramids. you'll level in no time [30 mins or so]
Next step i would change to a theif, pump my stats on agi and a little bit of dex, 15-20 dex, and level using the stilleto which the job changer gave me in payon dun01 until i'm ready to train in payong dun02. Oh and i'd carry some meat 100 or so and i'd also use the healing items which i collect while training, red herbs and red pots. I'd constantly earn high exp in here until about lvl 50. While lvling up i'll pump on agi and add a little bit more dex until about 25 or 30. By now i'd have a damascus and some good theif npc gears (theif suit, buckler, boots, etc)
Lvling is not such an issue here, i normally just go to tf02 and well i normally lvl my npc geared characters here till like... 80? sometime higher

The higher i've lvled in tf02 is my sin which is 96

easy class to lvl if u ask me

Oh and i never added any str until my flee was high enough to dodge most attack in tf02. Dex... i add until 40 only.
I dont know if you've chosen a second job yet or not but i normally go for a rogue cause of his auto-steal skill

great tool to collect cakes and earn some good money. I did this process till i got my ws gears completed except a lord kaho haha