Glads get both type of masteries. Stick with heavy, better in the long run.
While in C-grade, get plated leather (+4 str) only if you'll be in parties mainly. If soloing get full plate.
In B-grade, try to acquire BW (if you want, you will be able to keep going with BW way into the upper 60s, even higher, just get a focus Dual Tsu*Sls +4).
A-grade all depends on what type of setup you want (Majestic and Tallum are the popular choices among glads).
i'm only level 15 atm retrying the game after a 2 year hiatus. so it's ok if i only put points into heavy armor mastery later on and neglect light since i probably won't use it anyway? and that thing about duelists is just misinformation from the site class description listed on this site?
yes that will be fine, i'm lvl61 and have NO points in light armor, have used heavy thru out.
its really not misinformed, if you look at the light S-grade armor set statistics, they are very good for a DEX oriented duelist.
but you still have a VERY long way to go and LOTS to accomplish before you become a Duelist. just concentrate on getting the first class change done and then later on the second. stick with heavy, you'll like it.
last but not least, if you visit here (http://www.l2guru.com/forum/archive/index.php/f-25.html) and search for 'glad' in these 6 pages, you'll get enough knowledge on this class to last you a lifetime :) The higher you go in pages, the current the posts.