Unfortunately I don't know enough about these rifles to put that accurate a date, however based on my limited knowledge I do know that rifling was becoming popular (for the wealthy) in the mid-1700s, and percussion technology became popular around 1816 and later, so I guess that puts your rifle somewhere in the 1750s-1800s, unless someone more knowledgeable has a better guess (I am just doing a rough guess based on what little I know, my area of expertise is bolt action rifles).
100%. Also likely the reason it doesn't have a range elevation as your accuracy would be gone long before you needed to raise the elevation.
OP definitely a cool rifle, thanks for sharing. I really enjoy learning things about firearms that are outside my primary area of interest.