“Are adults still OK to tent solo? I love my Tiger Wall UL2, but am not thrilled with the idea of sharing it.”
Yes adults can be solo in a tent. There was a thread on tents at Philmont here on BPL just a few days ago.
“I have an Osprey backpack and include the 3l Water bladder. I see most using Smartwater Bottles? Are camel-back style bladders common or should I skip that if water is prevalent on the trail.”
3 L is a lot to carry. If I fill up on water at breakfast, I can make it to lunch with 1 liter or so. But you know your own needs. I think you see a lot of platyus bottles because they are lighter than many other commercial offerings. I use a 3 liter platypus hoser with plain cap (not the drinking tube) for overnight storage and 2 smart water bottles for during the day. I myself gave up hydration tubes because they freeze in winter and are finicky in the other three seasons.
You would also need to think through how you get treated water into the 3 liter Osprey. Most crews use chlorine dioxide pills. If the Osprey is easy to fill, you could have your crew water masters take charge of filling it at the end of the day and pitching the 3 chlorine dioxide pills with all the other crew water bottles and group water storage.
Issues like this should get sorted out during your three training hikes.