Yes you are right, if you book a round trip ticket it's more convincing for the bureau.

ummm, are you traveling around the world ?

Hello

I think your idea is funny , i would like to take a deep glimpse of it in the future

We spent a year traveling on one way tickets and were never asked to provide proof of an exit or ongoing ticket. (sometimes we had one and other times we didn't arrange our ongoing destination until after we landed in the country). We did, however have an idea of where we would likely go next so if asked we were able to quickly tell them our next destination- even if it might have been just a glimmer in our eyes.

We did not go to Central America so don't know if they're sticky about it. As you are able to return through Mexico sounds like a plan and an ongoing route...