I have a 2012 35QB4 -- which pretty much identical to yours as they made some more distinctive changes in the 2014 model.
Regarding your questions:
1. I have the docking station with 3 pull valves for the tanks (Black Tank, Bath Tank, Galley Tank). Can anyone educate me on what drains into each tank?
In your docking station, the 'Bath Tank' is the main shower and sink, along with the washer/dryer (if you have that option). THe black tank is the main bathroom toilet. And the Galley is the Kitchen sink ALONG with the rear bathroom sink.
I have two additional tanks in the rear, with those valve handles behind the rear wheel. One is the 'Black Tank' for the rear bathroom toilet. And the second is a 'Grey Tank' for my outside kitchen sink. (not sure if you have that option)
The Tank Monitor Panel in the rear bathroom is for the two rear tanks (or the one if you don't have an outside kitchen)
2. I have one additional valve, that I believe is for the second 1/2 bath, under the rear slide that has a grey handle , but there are two stickers above it. One sticker says Black tank and the other says Galley tank. Does the second 1/2 bath have its own black tank and the contents are combined with the bathroom sink? There is only one tank indicator on the wall in the 2nd bathroom. What exactly does this handle release?
SEE ABOVE ANSWER
3. Depending on the second question, is the black tank flush connected to the second black tank as well?
I have two Black Tank Flush ports within the docking stations. For some reason, FR installed them backwards. The forward port, is for the rear black tank. And the more rear port is for the front black tank. (hope that doesn't confuse you, I can add a pic if you like)
4. The trailer has a frame welded rear hitch that I believe comes from the factory. It is only a 1 1/4 hitch. Does anyone know what the weight rating is for that? I have a bike rack that would like to use.
Mine does not have a frame welded hitch receiver. I wish it did!
Best for you to contact FR for the weight rating if nothing is posted locally.
5. It has a water filtration system. Where is the best place to get replacement filters?
I get mine off of Amazon -- Walmart too has them.
6. Anything else I should look out for on this trailer?
We love love love the trailer...layout cannot be beat for us...all the new and other used 5'rs we look at, all pale in comparison with relation to layout and storage location etc...
I've done my fare share of upgrades and tweaks the past few years...lighting, converter, wetbolts, under-mount spare tire storage, dual fence post covers, upgraded the landing gear to dual motor and on remote control, LED throughout, second ducted AC, two bluetooth thermostats, LevelmatePro, and I could go on and on.......
We took it on a 6,500-mile, 32-day trip, August of 2018 out west to 12 national parks and more. Trailer performed flawlessly.
Only wish is that it had automatic levelers!!