Hi there, welcome to the form.
Playing a destroyer is a lot of fun and offers a fair bit of flexibility in builds, especially on normal difficulty.
1. There are 100 experience levels and 55 fame levels, for a total of 155 skill points to be allocated. But I think you begin with one in Slash already, so you get to decide on 154 of them(?). Plus you can find gear with +skills, so you can actually have more.
2. Just search each classes sub forum for build guides, I know for destro there's a good vhhc Spectral Echo build here viewtopic.php?f=18&t=8306
, and a Devastate build found here viewtopic.php?f=18&t=5133
3. Skill selection can be very personal, especially in the order of skill choice. On normal difficulty you really can just put them just about anywhere. This game is pretty forgiving in build design and you'll have a hard time creating a character that's unplayable.
Keep in mind that this is just my opinion.
Firstly you are correct, Frost Shield should be on your list. It is the best skill for survivability, and really helps keep you alive. I like to max it as soon as possible.
Dual Wielding - You can read my thoughts here viewtopic.php?f=18&t=10327#p96089
, bottom line, unless you're using the normal-attack/Spectral Echo for the majority of your attacks, you really don't need this skill until you've maxed everything else. That isn't to say that you shouldn't carry a weapon in each hand though, Slash and Devastate both benefit from 2 x 1h weapons.
Adventurer - Sure, but not all that important IMO, I'd put points in this after Treasure Hunter. If you start to out-level the floor you're on this game gets way too easy.
Critical Strikes - Great skill
Treasure hunter - Another good skill, if not only for the gold find thogh. The gambler is your best place to get uniques and sets, and Barter is the skill that will reduces the prices in shops and at the gambler, and will convert your loot to more money.
Martial Weapon Expertise - Another solid skill.
Block and Perry - You actually get more block out of Shadow Armor
Armor Expertise - I max this first
Pet Mastery - I've never used it. But it'll help with town travel time and if you want to use summoning spells or let your pet do a lot for the dps, sure why not.
Barter - See above
Slash Attack - You really only need one point in this. That will do just fine until you get Spectral Echo or Devastate.
Titan Stomp - Is another one-point-wonder in the early levels, but since you're almost at SE and Devastate its not really worth it.
Spectral Echo and Devastate are the two most commonly used high dps attacks. Read the linked guides for better advice on these two skills.