You've got the right idea. Build small, hidden, don't harvest trees and rocks near you, they won't come back. Plant x and turrets will probably only serve to give away your position, as they fire on people flying by that might not otherwise notice you. Although turrets inside the base are always a good idea.
3x3 is probably the smallest functional base you can have if you want a fabricator and maybe a generator/turret, but a primitive base can be much smaller.
This trick has saved me so many times...keep a cache of items hidden. Ingots, tools, cp whatever. Your most valuable things should be hidden when you log off. This can be done a couple ways but my favorite is this...pick a foundation inside your base that won't be covered (if it is 3x3 you'll want to use the center one). Demolish it, place 4 small boxes down there and load them up. Then replace the foundation. Most people aren't going to foundation wipe a base, they'll just bust in, take what they see and go. That being said, leave some things out to make it seem like you don't have much to loot. Alternatively you could hide this set up in the woods. But make sure you snap a second foundation to it! Single foundations will auto decay very quickly, leaving your boxes sitting there exposed.
Some of my best ark adventures were in a setting like this. It's a rush to know that just being seen could be the end of you. It's living on the edge of Ark. When you get ready to start killing players and dinos, go on YouTube and search "one wing unconventional warfare ark", that dude has some stellar ideas.
