1st off, it's NOT legal. You risk a ban. As others mentioned if you pay with plat, you can consider it a gray area but if you pay with real money it's not in the gray area anymore.
2nd Getting GWAMM and 50/50 it's both a lot of work and two different things.
GWAMM refers to a title. If you wish to achieve GWAMM you can do it yourself in maybe two months if you play a decent amount of time (2-3 hours per day) AND have some helpful items (such as : summoning stones, consets, buffing sweets, etc.). There are some tips for the choices you can make on wiki
http://wiki.guildwars.com/wiki/Kind_of_a_Big_Deal although you will have to pay a bit for the consumable titles....[personnaly I farm GotH(Gifts of the Huntsman) in pre-Searing, Gifs of the Traveler for consumables points, although it might take some time]
50/50 okay...I honestly don't know why you would want such a thing...did you at least complete 30/50...30/50 is doable in a few months as a new player, providing that you play enough and you get accustomed fast with the game itself. 50/50 is quite an ambitious project as you need a ridiculous amount of money to get it, not to mention that you won't get anything amazing for it....just some titles that don't even give boosts. They are just for fashion, nothing more.