Fighting more opponents is always difficult and a big challenge
You have less time to do all the actions which are necessary.
Even the power distributor handling is more challenging.
In view of heat sinks they have many tasks:
1. When shields are gone, activate one to hide from sensors and decrease the time you are vulnerable, care in light of emissive weapons though.
2.When firing srb rail guns and using heatsinks: it not only cools down the ship, but it also loads the distributor a little, so use one heatsink and fire multiple volleys of rails when you are in a good attack position ( < 1 km). Remember the srb damage falloff starts at 1 km and at 1.5 km the damage is zero.
3. If shields are still up and you are under heavy attack and getting a lot of damage, you can use a heatsink to hide from the sensors of the opponent and also lessen gimballed weapon damage, here also be careful in view of emissive. Also, rail gun snipers are also not as able to destroy your modules because when you are cold they are less likely to get a lock on them
now chaff
Chaff is a specific counter weapon; if you get a lot of damage from multiple attackers activate it.
You can increase the time they confuse the enemy's gimballed weapons by flying through the chaff projectiles after launching them. I believe this is shown partially in the video. Because chaff have a cooldown, take 2 of them so that you always have chaff available when you are getting heavy damage.
Chaff are highly effective versus gimballed multi-cannons and lasers, they are not so effective versus frags. Frags can hit even when using chaff because the enemy is usually nearer and frags spread a lot... therefore you will be hit, perhaps not with the full volley but it will hurt nevertheless.
Fighting more opponents is the best drill to get better in 1v1 because you have to do everything in a shorter time and be much more accurate.
