Uh, RC is our only viable AOE* skill for mobbing and fast killing. Taking that into account...
1) Any katar that you can get your hands on (people often use hunter fly carded jurs, elemental katars, anything really that'll help you kill faster). For general purposes, a Durga or Wild beast claw (you can enchant it in malangdo) is probably your best bet. I wouldn't recommend DD for leveling but if you want to try it, who are we to stop you.
2) Sticking to the hbp bonuses is in general a good idea. so 90 agi/vit/str/luk with some dex mixed in is good (RC needs dex to hit, I usually start with 40 dex first then add more if I feel I need it). Note that I put the stats in order of what I would get to 90 if I would level a gx now, learn from my mistakes. :v
3) Uh, no idea about your budget, but something along the lines of: HBP, Variants, WPH+Alarm/Rudolph/Fish in mouth/RWH (if you go for hunter fly cards, you will need pots with the rwh in sticky situations or just fwing away? idk how you play), elemental armors (Nab's with fs enchants is good, "easy" to get can be time consuming tho, I often use glit jackets cause I didn't have money at that time). If you have hp consumables to spare, a +7 Drooping alicel would be awesome. You can always swap headgear to adjust to any situation tho. BDM can be pricey for mid, I still can't find my dark pingu sunnies, that is also an option for mid. For lower headgear, pirate dagger, gangster scarf, the lucky clover, basically whatever you can afford. :x
For accessories, Rogue's Treasure, Bradium Brooch, Assassin cuff, Vesper core 04, same as low and mid headgear, whatever you can afford and whatever will help you stay alive/level. ._.
* You can use meteor storm/grimtooth but those are slow as hell to level with from my experience. ._. Didn't try venom splasher, I mean, from the RoR it seems fun but nothing more.