I’d worry about the scale and defense capabilities of a small nation like Costa Rica. Larger unfriendlies nearby, both north and south, perhaps easily overrun.
You’re right. They have no army. And Nicaragua in the North is always in a bad mood when it comes to CR. The Nicas come across the border to work and the Ticos treat them as illegals. But Panama in the south is very friendly. And well armed with American weapons. Plus we land Marines in the ports of CR from time to time for drug interdiction. And the terrain is similar to Switzerland - not easily overrun. And there isn’t much for an invading army to steal....mostly farm lands and crops. I wouldn’t worry about that.