1- skills. all the same for all races. all classes can access the close range and long range skills. the magic skill.. i think doesn't get unlocked till you're 40. there's 4 lvls of skills. Basic, Expert, Elite, Master. Basic skills are available right from the start. Expert doesn't get unlocked till your 30. and the rest of it, i don't know.
For Force skills, you have to buy them from the Force NPC. The spells for both bellato and cora are basically the same, except that Cora are the only ones that can use Dark force and Bellato are the only ones that can use Holy. Tier 1 Force spells (basic) are around 53k each, Tier 2 (expert) are around 230k each. and Tier 3 you can obtain via monster drops.
as for what leveling does to the skills, i have no clue. i honestly have never seen a noticable enough difference in terms of power, except that for buffs, the higher the level, the longer the spell will last.
2- races.... you basically just listed them =/ accretians for me are the best with melee.. and cora with magic. bellato somewhat in between.
3- basically almost all classes between all the races are the same. though once you get a "new" class, i think only 3 new skills are added to your list. there's really no classes restriction as long as you level the necessary PT, you just don't get the skill of that new class (job change at 30 and 40)
4- i don't think you're able to make intense weapon... though i'm not really sure on that. basically... you just keep on crafting items so your crafting PT goes up.
http://rfonline.x2game.com/GameInfo/Item/OverView.asp if you go to that site, click on any of the sections (armors, ammo.. etc) it'll give this huge list of all the items in game. click on any of the individual links and it should have a pop up. That pop up window tells you what is needed (though it's in korean.. so who knows.) and at what level you can craft them (craft PT level that is). as for the ingredients, the higher items (after craft pt 12 or so) you'd have to buy from players, you cannot buy the needed items via the npc.
5- you need the upgrade tool kit. buy it at your npc. i know it's the talic... though i've never heard of using ruby and such, perhaps it's the same way with talics. just buy the Upgrade kit from sundries, use it.. and drag and drop your weapon then the crytal or whatever. it'll tell you if it's not able to upgrade. (there's also a chance it might break or unsuccessful or something.. )