Even though EZE has three different check-in and arrivals "terminals", all of them are under one roof and, if staying airside, you can walk freely from the first gate to the last without any issues and controls.
Here is a chart of EZE courtesy of Aviacionline:
https://aviacionline.com/wp-content/...eiza-plano.jpg
Active runway is usually RWY11. It is the longest and has the only CATIII ILS. If weather is clear (most likely by this time of the year), they can switch to RWY29 depending on winds. EZE has an old runway layout and as such all runways cross each other -- this is 1950s airport design, so planes could land irrespective of wind directions. The problem, however, is that two runways cannot be simultaneously active, as planes risk crossing one another. So if 11/29 is active, no need to worry about 17/35, as 99.9% of chances are it will be closed.
The closest gates to RWY11 are those in "terminals" B and C, i.e. gates 14, 15 and upwards, close to the Aerolíneas and LATAM lounges. The runway can be seen from a distance (remember there's the parking platform in between). From there you can also spot the edges of former RWY 05/23, which is where --they say-- VIPs will park.
For obvious reasons I have never changed planes at EZE, but I would double check if you don't need a boarding pass for a connecting flight in order to enter the transit area. Landing passengers are directed through a long corridor directly to immigration and customs, so unless you can use the transfer lane you won't be able to reach the airside area.
As for public transport in BA during the summit, yep, it's going be chaos. There's another thread on this forum where it's being discussed.