where and how many pellets should i put into the coolant?

They go into the radiator, preferably the lower radiator hose. If you put them into the coolant tank, they will just settle to the bottom and possibly clog the hose.
I'm not sure on the number of tablets to use, ask the dealer.

Remember that the cooling systems are different between the HT4100 and a Northstar....

cadeville has an HT4100 I think. The coolant supplement pellets go into the radiator at the pressure cap fitting on the radiator. If you want to take the hose apart and put them in there it is fine but you can just put them in at the radiator cap. You will have to crumble the pellets up to get them into the radatior end tank as there is not enough room between the tank and the trans cooler inside the tank for the whole pellet.

The Northstar needs the pellets put into the rad hose as there is no rad cap on the radiator itself and the Northstar has the pressurized surge tank that you do NOT want to put the pellets into as it may clog up the hose to the water pump.