Technically yes, but it will probably be pretty boring. There is currently no AI to play against, and tribes do not spawn as part of Worldgen. RTSCraft is intended to be played in multiplayer.
In a future release, the RTSCraft team may implement a Wave Survival gamemode. For details on this, see Issue #102.
2. I installed the mod, how do I get the maps?
Maps are not included as part of the mod download. You can make your own, or check out the maps wiki page for some examples.
3. Does your mod work with X mod? It's my favorite!
RTSCraft was developed - and meant to be played - by itself with no other mod interactions.
That being said, it may work with your favorite weapons mod or magic pack or whatever, but adding new mods introduces many ways to "cheat" during an RTS game, or new ways to crash Minecraft itself. Here be dragons.
4. Can I change the weapons/skins/buildings of each tribe, or add my own tribe?
Unfortunately, this isn't possible in the current release. Assets are fixed within the mod download.
In the future, the RTSCraft team may allow for custom "asset packs", but doing so introduces yet another variable in the balancing act of the (already complex) system. For example, even without changing the footprint of a building, just changing positions of the target entities can make a certain structure more defendable. It's unlikely this level of customization will make it into a release.
If there's one particular asset you're interested in changing, check out the Tribal Theming Issue or create a new issue with your proposal for changes. If you want the stables to look different (keep in mind it must have the same footprint), show us what you think it should be, don't just say "Blue stables are ugly, plz fix."