For Brazil:

Put the 6 and 8 size armies on defend front order and use the size 4 army to naval invade grao para, then move everyone down to crush Rio grande, you can naval invade them too if you want

In general:

Don't attack unless you have overwhelming strength (30+), or you are more capable of sustaining attritional warfare

Spam generals to get pillagers, arty commanders, and offensive strategists

Use heavy barrage and pillage over the normal advance whenever possible

If your opponent has a coastal capital attempt to naval invade it once they dedicate their army to a frontline

Navies are king, you want to have army parity with your rivals, but you need naval supremacy. Raiding convoys not only destroy your opponents economy but also directly stop their army from resupplying at all. They will start to take heavy attention and will get pushed out even by 1 irregular