What I've got planned so far: Invest in sneak, lockpicking, speechcraft, bow, alchemy, light armour, light armour smithing,.
Not sure about: race, melee weapon (thinking dual one-handed (does onehanded include daggers/what are the advatageuos of daggers?)
Thanks!
You want to be a dagger specialist.
1. Sneak
Yes sneak is compulsory. There is a perk that gives daggers a x15 damage multiplier for sneak attacks.
But you pretty much need all the perks to be able to get close to enemies for the sneak attack in the first place.
2. Bow
Bow is needed because I still don't know how to sneak attack flying dragons. So you need it for dragons.
Use bows at the start, before your sneak reaches 50 for the x15 dagger perk.
3. Smithing
Yes smithing is nice, but not for armor. You want to smith and sharpen the best possible dagger for your sneak attacks, so that your x15 damage multiplier will 1-shot enemies.
4. Light Armor
This one is probably for dragon fights only, or the rare situations where you cannot sneak attack something. If you 1-shot your enemies, that means you won't lose a single health. So no point in having a high skill in light armor.
5. Alchemy
This one is nice for the various poisons, such as the paralyze poison. But I rarely need to use it because enemies die in 1 hit. It can be useful to make the potion that allows you to carry more loot.
Poison that damages health unfortunately does not get multiplied in a sneak attack. Enchantments also do not get multiplied/
6. Speechcraft/Lockpicking
So far the speechcraft skill just saves you money, whether it be from trading, or in situations where you can persuade someone to reveal information instead of having to pay them money.
Lockpicking may be useful to pick treasure chests in dungeons.
7. One-handed
You may want to consider the one-handed skill, at least the first perk of it. It will further increase the damage of the daggers, and that gets multiplied x15.
Pick any race you want.
For weapons, dagger is a must for sneak attacks.
Use a sword or bow for situations where you cannot sneak attack.
So far I have recommended these for combat. I can 1-shot anything that I can get close to, giants, sabretooths, bears, etc.
I assume you play a thief for combat and not to steal things from people's houses.