Make sure your TA knows that you are not willing to take the risk of Argentina resident fares - you can end up with nasty surprises when you check in.

What carrier are you flying to/from North America? Are you sure LAN doesn't fly all the domestic segments? You can buy a South America airpass if you fly in on LAN or a Oneworld carrier. I don't know what kind of pass (if any) AR offers. If you fly AR, allow a LOT of time cushion, if the amount of time cushion of needing to get to a connection, or to a place on time, is important. Your TA cannot help you with the airpasses, because they cannot be purchased in Argentina.

Also, see how your trip prices if you try and book all the segments in one ticket. You might be surprised - it might be less than if you buy the int'l as one and the domestics as another. It could also work the other way. But you could theoretically end up with a better baggage allowance on some segments. Just something to think about.