Creating a Rust map is one of my favorite things about being a Rust server admin. I can create a Rust world in seconds by simply plugging-in some random numbers (map seed and map size into the config). Here I'll explain some of the ways I choose the best Rust maps for my own servers.
The 3000 - 4000 world size range works for most popular 100+ player servers. I've found that this range is ideal for "most" consistently high-pop, 100+ player servers. I would not recommend this size for solo, solo-duo, solo-duo-trio, or for most regular vanilla Rust servers just starting out. This is because during low population periods players will grow bored of traveling the expansive nothingness to find other players. Large maps can feel dead in low-pop periods. This leads to lower player retention. The minimum size I would start with is 3000 or even smaller. For example, I am currently running a new solo-duo server with a relatively low population average 20-30 players at any given time. I've found that even when player numbers spike higher, that the real sweet spot is always a 2700 world size. So if you are running solo, solo-duo, or even a solo-duo-trio server, or a new server just running vanilla / no rules Rust, then I highly recommend a smaller size like this IN MOST SITUATIONS.
The Steam Controller
Not a fan of controllers in general, and am a dedicated PC mouse-keyboard gamer, but this device worked well for me. Very interesting new experience. The device has an excellent key customization.
One particular map on a German server (when I was a noob) has influenced how I choose maps for my community today. This German server map provided dramatic terrain variation that included ways for making a safe passage from a resource abundant and isolated wilderness, to several important monuments. This safe passage was afforded through a particularly large mountain range. The mountains nearly divided the map and stood as a kind of barrier against many players that tend to find them more of an annoyance than a strategic advantage. I rarely encountered any "run & gun" players or clans while making passage through the mountains. As a result of having fewer encounters and thus keeping a low profile, I was able to create a significant stronghold with my stockpiled resources. This gave me time to grow strong and to eventually dominate the server. Time + isolation is all it takes for solos and noobs to put clans out of business completely. So when I choose a world seed I always consider my past experience, and weigh choices in the favor of solo players and noobs. Afterall, they are at the core of any truly balanced server.
Choose a map with a large mountain range that divides monument areas from pockets of resource rich isolated regions. Clans and "run-and-gun" players may not like it much, but noobs and solo players can at least have a chance to flourish. Please note that huge mountain ranges at the time of this writing are generally only found on 3000 + world sizes, but smaller maps can be found that include enough terrain variation and smaller mountains that do just as well.
Islands are not very popular with clans and "run & gun" players that tend to gravitate near monument areas and prefer not to swim. Experiment with islands. Or islands plus mountains might do the trick.