Welcome to the forum. Bengals are not like your ordinary cat. Are you thinking about a kitten or an adult bengal? There is a huge difference. First to your question about letting a bengal outside. Many bengal owners do. If you're on a large property with no neighbors or roads in sight, maybe. Does it make your bengal happier? Probably! Who doesn't want to run free. Toddlers love the challenge, too, but one would never let their two-year old outside unsupervised. Trackers can give you better peace of mind, but bluetooth trackers re useless unless you come into the range of the cat.
Are indoor cats miserable? I highly doubt it. You have a large home with lots of roaming areas. You could create a catio or cat enclosure that would allow outdoor access for your cats and keep them safe.
I do question when a bengal owner makes a huge financial investment and then simply allows the cat to roam free. Regardless of whether your area has predators (coyotes, foxes, large dogs, other tom cats) running wild, bengals get hit by cars, get stolen by people who can't believe they are actually looking at a $$$ bengal and want to take it.
Whether a bengal will get along with another cat is an IFFY question. Your current cat may be territorial and not want another cat or kitten to enter. Some cats understand a kitten more than an adult, but it's really the personality of the cats. You have a large enough home to separate them initially and slowly introduce them to each other and there is plenty of room for each to have their own territory. Just know that bengals need a lot of vertical space and both cats need room for their own territory. It is usually coin toss as to how they co-exist with each other, but I do believe most do well together. Just be prepared to spend time and have lots of patience as you try to get them to behave around each other.
Bengals are loving, loyal, intelligent, energetic, vocal, social cats. But we LOVE them.