Here's the basics on equipment...
Any character can equip any weapon/shield/focus. However, some equipment has an attribute requirement. While this requirement will not stop you from equipping and using the item, you will not be able to get the full benefit out of the item if you don't meet the stated requirement.
For example, a sword might have a requirement of swordsmanship 7. Even if you don't have 7 ranks of swordsmanship, you can still equip and use the sword, but you won't be able to get full damage out of it.
Armor however, is profession specific. You can only wear the armor of your primary profession, so a primary monk can only ever wear monk armor. You can also only upgrade your armor with runes and insignias that are of your primary profession (or those that are classed as common, that any profession can use). For example, as a monk you can use monk specific insignias and runes to boost your monk attributes, but you cannot take runes designed for something like a paragon and use them on your gear. Runes and insignias are usually labelled with the profession that they're designed for, and if there's any doubt you can visit a rune trader, where all the runes/insignias on sale will be sorted by profession.
As to your question about levelling, you will find that you'll reach the level cap relatively quickly. Guild Wars is designed to reward player skill more than player grind, so you will find yourself at the level cap and be able to afford max equipment relatively quickly.
Also, as you're a new player I have one major piece of advice for you: visit the
Guild Wars Wiki and be sure to add it to your bookmark list. This site contains pretty much all the information you will ever need to know about the game, from armor arts to mission guides to skill data and everything inbetween. The site also has a section containing guides specifically written for new players such as yourself.
And if you have any other questions, my IGN is listed under my avatar here. Feel free to hit me up in game anytime if you find yourself getting stuck on something, or if you'd just like some company as you get used to the game.
). I used to be an end game raiding priest from WOW and enjoy playing a support class. 
