I have read that once a FO gets to 1,000 hours, they are automatically sent to upgrade to Captain. How does the captain upgrade work? For example, how are the aircraft type and base assigned? Is it just based off seniority of those in the class, and if so what does the usual class consist of (% 175, % 145) and I assume the near entry and direct entry guys are all low/no time seniority?

Some people post about upgrades as early as a year in, while others are closer to 2 years. Is it smart for someone to bid reserve for a few extra months to gain more seniority when upgrading (in order to get the base you want?)

Aircraft and base is all seniority based. You get what you can hold. 175 tends to go senior, esp DFW. 145 gets the rest, split by DFW, LGA, ORD, MIA. MIA and DFW are more senior and rarely come up for bid.
How quickly you get to 1000 depends again on equip and base. 175 FO’s have easily been ready in less than 2 years. 145 guys are over 2 years on average. And yes, lots of guys leverage reserve to adjust their arrival at 950 hrs if they can.