GD is guild dungeon. Luina is best all around. My suggestion would be to join a guild for access. If you wanted to WoE then you'd have the ability to, but I doubt any guild would be opposed to somebody just farming GSB (especially if you gave them a few). If you need help with this feel free to PM me and I can point you in some directions if your looking for GD access.
Only one bison. Ideally you'd go for Bison + BSB/Shackles. Bison w/ mantis works. The last +1 str bonus comes at job 70 or something, so it works. I later (post max job) switched to a nimble bison for faster cast time. The bison works best w/ thorny buckler (obviously), but thorny bucklers are expensive and it will just be a quality of life purchase vs a "necessity". Bison isn't bad in general cuz of the slot + the 2 agi.
If you get a blue twinblade then you'll need to fire endow for GD. Not the biggest deal in the world.
If funding is an issue, just leave the Valk Mant at +5/6. Even +4 works if on a tight budget. The damage reflected doesn't matter, its just the hit from the reflect that does.
Next protip move would be to make sure you have a soul linker on another account.... This is how I roll with it. I bring the SL down to GD and let it die. When it is needed I'll clear the mobs nearby and res it via Ygg Leaf. I'll do 1 hand quicken. Right before the soul link is about to run out I'll do one hand quicken again to keep the buff up as long as possible. It will buy me 5+ min every time I res the soul linker. Soul linker doesn't need gears or stats, just make sure it has knight link.
Sidenote: Dex and ASPD are HUGE for spamming BB. A built with 1 agi can get 184 ASPD w/ basic foods, one hand quicken, zerk pot, thorny buckler set, and NO bless/agi (important to me).