As to type of antifreeze to use, Honda states to use silicate free mixture as silicates will eat the waterpump bearings and seals.
You can buy gallon of Honda antifreeze at the Honda car dealers for $20. Premixed.
Quarts at Honda m/c dealer for $5-$7. Premixed.
Some use Peak antifreeze as it states it is sillacate free.
I get the full strength gallon ($12 walmart)) and mix it 50/50 with a gallon of distilled water($1)
I use Maxima premixed coolant made for motorcycles I get it at a local Cycle Gear. It's not that expensive and only needs to be replaced every 2 years. I would not flush out the cooling system with anything but distilled water, unless it is already plugged up with corrosion. Hopefully not. When I first got mine, I went through a long drawn out procedure, by draining the coolant, filling with distilled water, riding it a few miles to circulate the water, then draining it and doing it all over again. I did this about 5 times until the water came out clear. Then I drained it and put the coolant in. Don't forget to remove the overflow reservoir and clean it out. Toilet bowl cleaner is good for removing any rust or scale from the plastic reservoir, but do not put it in the engine.