Motocross training is great but I think our guy is ALEADY there, yes? Bit late for doing motocross and with a first timer I'd not jump straight on a Moto bike ... too early. Got to learn basics FIRST. (I taught many kids to ride and taught old guys to ride off road) Riding round S. America is not a Motocross race anyway ... about 70% paved roads and passable all weather dirt roads. Not really that tough unless you go LOOKING for trouble following Cow Trails (Llama trails?)

Can you ride a bicycle? Are you in decent shape? Decent balance? Good, then you can ride a 250. Get a GOOD ONE.
Enduro style preferable for travel.

City Traffic will be biggest challenge/danger (in a car as well). So your defensive driving (riding) skills will pay huge dividends. You get no 2nd chances on a bike. One good shot ... your dead or ruined. As long as you know that fact. Equipment helps but won't always save you. Boots, helmet, gloves at a minimum. RAIN GEAR!

Get the bike then get out and practice some basic moves. A must do.
1. emergency braking. Braking should be 2nd nature, something you don't have to think about. Use BOTH brakes together ... but the front is the important one for stopping fast. Go light on the rear on paved roads and don't use it in the wet.

2. learn to swerve and avoid rather than locking up brakes and sliding into a car or obstacle. Remember! On a bike you WILL GO WHERE YOU LOOK!
So ... LOOK around the obstacle DO NOT target fixate on it like MOST do.
Look for a path around the obstacle. This can save your life.

3. Learn to start and shift the bike properly. Do NOT abuse the clutch.
4. Learn to and get comfortable with leaning the bike WAY over in a corner. Once again LOOK WHERE YOU WANT TO GO ... and you will go there! Do not be afraid to LEAN the bike over ... way further than you feel comfortable with.
Look through and around the corner, look towards the exit of the corner. Always maintain proper tire pressure. Very important on a motorcycle!!!

5. Learn the limits of your low powered bike. DO NOT make stupid passes. This can be a dangerous game. So start nice and easy until you really learn the bike and develop some skills. Skills will save your life.

6. Learn the limits of the bike, learn what it can do and what it won't do. Ride within your and the bikes limits. Push yourself to PRACTICE the basics outlined above. You may survive.