A classic Ranger sounds good to me, but if you want to rely heavily on ranged weapons, you should play an Archer. There are only two drawbacks: 1) you can't wear heavy armor, which isn't a problem since you want to use stealth and wear leather armor anyway like a good Ranger should, and 2) you can only put one proficiency point in any melee weapon, which doesn't really make much difference in the long run. An Archer can decimate entire parties of enemies before they reach you, so there doesn't have to be much melee fighting in the first place. Called Shot and grand mastery in ranged weapons more than make up for those drawbacks.
Contrary to what your friends say, I think it is harder to use melee weapons early in the game than it is to use ranged weapons. If you use disabling spells such as Sleep, Horror, Glitterdust, Web, Stinking Cloud, etc., ranged weapons are a very good bet.
Later in the game, at really high levels, I think that ranged weapons and Archers lose some of their appeal. But so do single-class Rangers, so you shouldn't let that discourage you from playing an Archer.
Throne of Bhaal adds many new things the game, including several more chapters and a brilliant conclusion to the saga. (Surely you want to see how the story ends.) It also adds a higher experience cap, High Level Abilities, new items, and new dialogues. I wouldn't play Shadows of Amn without it. Try Greater Death Blow in combination with an arrow of detonation and see what you think.
I don't think it's possible to attain Grand Mastery in Longbows, Short Bows, and Crossbows simply because you won't get 15 proficiency points to distribute. If I had to choose between, personally I think I would pick Short Bows just because there are several short bows that don't require ammunition, which eliminates some of the difficulties in managing stacks and stacks of arrows. Throne of Bhaal has an ammo belt that makes it easier to carry arrows. You can also use the unofficial Ease of Use patch to increase the capacity of bags of holding (so you can store thousands of arrows instead of just 700) and to increase the number of items you can put in one stack. I wouldn't play without it. Ease of Use will also allow you to wear rings of protection even when you're wearing enchanted armor, which will improve your armor class.
As Amran_X_Kaiser suggested, you should definitely make use of your spells. Doom can be used in combination with Greater Malison and Glitterdust to give your enemies huge saving throw penalties. And you will definitely want to use the High Level Abilities offered in Throne of Bhaal.
I don't think you should worry too much about specific items before you've even started the game. Too many people spend too much time worrying about "I want to max out out my character so what items should I get?" There are plenty of great items in the game and it's really hard to choose between them, so that should tell you that you'll have great equipment no matter what you choose.
However, if you want specific suggestions, I would choose the Tuigan Short Bow in Chapters 2-5 with Arrows of Piercing and Arrows of Fire, the Short Bow of Gesen in Chapters 6-7 in combination with enchanted arrows (you can do that even though it doesn't require arrows), and then in Throne of Bhaal you can choose another short bow if you want. As for armor, I like Aeger's Hide and Corthala Armor if you can manage to wear it. Shadow Dragon Armor is nice, but the best leather armor in Throne of Bhaal is Ice Dragon Armor. For a melee weapon, I'd pick one that inflicts elemental damage, such as the Stonefire Axe or the Hammer of Thunderbolts (which can be upgraded to Crom Faeyr). If you dual wield, you can put a weapon in your offhand that confers special benefits. For example, Belm grants you an extra attack, and the Defender of Easthaven gives you resistance to damage. Celestial Fury is also great if you don't want to give it to one of your other party members. If you pick a two-handed sword, make sure you put a couple of proficiency points in Two Handed Weapon Style. Boots of Speed, the Cloak of Non-Detection, Girdles of Giant Strength, and rings of protection, fire resistance, free action, regeneration are also good choices.
