Fast metabolism and cardio for health?

[Paradise-Bodies]

Hi,

in 15 years of bodybuilding i never did cardio except before a competition.
Now i'm 30 and wanna to cardio for health and endurance.
But i'm unsure what would be the best.

I got a fast metabolism and need min 5000 calories to gain weight and my split is
two days workout, one day of.

So i to cardio just on of days what means i got only to units a week (enough?) or after my workout (what means i don't get my carbs and whey right after)?

Heart rate? I think 60-70% MHR would be the choice.

[Paradise-Bodies]

Nobody?