You're level 10. I play on Master difficulty. I'm over level 10 and I can get 1-shot by a sabre. Some enemies you need to just bypass until you're a higher level. The only thing I do right now with giants is run away from them. As for 10 arrows vs. a spider-- make sure you're always looking for a more powerful bow, and when you're in town buy the most damaging arrows you can. If you're always using iron arrows, you're not going to do a whole lot of good. Pick up appropriate perks. It doesn't take long to get the x3 damage multiplier from the bow, which is awesome. Even on Master difficulty, it isn't long until you're 1-shotting groups of enemies with an enchanted bow and never be detected.

I'm using an Imperial bow with steel arrows. It just took me 12 arrows to down an orc on the path to Riften (omw to join the thieves guild). I had each arrow fully pulled back but didn't get a sneak bonus because I was found first. Btw, how does an assassin travel around fast? Do I have to literally sneak across the road? Seems like it would take 30 min - 1 hour to get anywhere significant.

Another thing, as an assassin every single person I come across I usually kill (in the wilderness). I'll usually save the game, kill them, loot, then google their name to find out if I've killed someone useful to me or for a quest. As an assassin I can't afford sheathing my weapon and walking up to someone and having them be hostile and/or a bandit (I've not played Oblivion and don't know all the armor types yet). Am I missing the ability to see them closer or a friendly/enemy icon? It seems like if you're in assassin the rule of thumb is to kill everyone you meet in the wilderness or risk being killed due to missing your sneak shot.

Advice?

Yeah, awesome advice for that situation. Stay at a safe distance in sneak mode, and fire an arrow near them, if they turn red on your compass, just wait until you're hidden again and attack. If they don't react, they're friendly. That's always what I do when I approach from afar and aren't sure.