Welcome to the Truck Camper world! You will find that a TC is an optimization problem to be solved, more so than other types of RVs, due to size and weight (and budget) limitations. You need to find the right camper for _you_, depending on how many people want to travel where, when and for how long, what their personal preferences are during a typical day in the RV, if you want to take any type of gear or a trailer along with you, and a number of other aspects. There is no "best" TC out there for everyone, but there is a "best" TC for you that is the best fit for your needs and wants and possibilities.
Your question is a bit unspecific. What do you want to know about all the listed topics?
I know the search function here is not the best, but you might still try to see what was written about different topics in the past. There is also a buyers guide at the truck camper magazine website that may give you some helpful input.
As an example, you will find that there are just a few tiedown systems - Torklift makes a quality product that is not cheap. Happijac makes another one that is different in design and works well for many. Some people build their own version of the Torklift frame mounted system and are happy with that. All of them will work fine if installed and used correctly. There are a few more offerings out there.
The jacks these days come from Happijac or Rieco Titan. Used campers can have the discontinued Atwood jacks or an older version of the Happijac motors. All will work, all have potential to fail. Electric jacks are very convenient, especially if you take the camper off the truck frequently. If you just do this once a year, a good cordless electric drill may work well for you at 1/4 or less of the cost.