The Royal Mercury is a private label Silver-Seiko manufactured in Japan. As such it's a decent portable and I'm sure you'll find it enjoyable to use. Yours appears to be in above-average condition - it still has the original shipping restraint for the type bars - and it might just be that it was never used, so you paid a fair price for it.

​As for resources, you've found it; there are a number of experienced collectors here that would be more than happy to help you out with any question you might have. You can make use of the forum's search function to find previous posts containing specific keywords.