Green Man, congrats, it sounds as though you have National type resonator guitar. Many Blues players choose to play a National style resophonic guitar. It has a similar but distinctly different sound from the Dobro type resonator guitars.

Know that string choice is generally a personal thing, but as others have already offered, it can also greatly depend upon how you choose to tune your guitar. A standard tuned guitar can generally use most any standard set of strings but when you alter your tuning to open tuned forms, sometimes it can require a customized set of strings. Many string makers offer their own custom string sets but you can also play with various string gauges until you find what suits your needs.

Different materials, used to make strings, can offer different types of responses, from mellow to bright. I like my strings to sound bright. The perspiration in my hands can dull a set of bronze or brass strings quickly. So, I use a nickel wound string. Actually, I believe these are merely nickel plated. Normally, nickel type strings are used by electric players.

Though my homemade 'Nobro', my own hybrid of the Dobro and National type resonator guitars, has a pick up on it, I rarely plug in. My Nobro has a square neck but the strings are not raised. The action is high enough for me to play bottleneck slide but low enough for me to also add modified chord shapes in the open tuning I use.

How you choose to tune your guitar is determined by the kind of music that you wish to explore. I enjoy playing bottleneck slide Blues. Many of my friends chose to explore the open G tuning that many early Blues artists used. I wanted to try something different. So, for the last 30+ years, I've been exploring an open E form of tuning. I've just recently started exploring a slight alternate to that tuning, open E minor and I'm very pleased with the difference that even this slight change has made to some of my songs.

I modify the open E tuning that I use. Though the form is the same, I'm generally tuned four half steps high of E, in open Ab. Because of this alteration, the tension on my strings is near their breaking point. This also exerts an enormous amount of pressure on the cone that I use, a Dobro type Quarterman brand cone. I'm happy to say that my cone has held up for over 20 years under my punishing approach to tuning and playing.

It's the amount of tension that the strings place on your particular cone that is critical to how well your resonator will respond. There is a fine line between too much tension, just enough and not enough. Finding that sweet spot takes some work. Getting the help of someone who can set up your guitar so it can respond its best, with the type of strings you choose and in the tuning you wish to use, is good advice.

You might alter your tuning to suit your vocal range, though in many cases a good quality capo can assist you in this.