Again, assuming you were serious.
Now would you suggested that:
1. I take off the mowing deck with brush hogging?
It depends on what you are mowing. For grass, fairly short weeds, I leave the MMM on. For true brush, take it off, but be sure you have a HST fan shield from Bro-Tek or you can make one as the HST fan is vulnerable and is a bear to replace.
2. Or the brush hog with mowing?
Yes, take the bush hog off while using the MMM.
3. Or the loader while mowing?
That is open for debate. I always take my FEL off for MMM use. I use my FEL for counter weight when bush hogging up inclines as well as to use as a feeler for obstacles etc. It will make your tractor more tippy, but since you already own a tractor you will be familiar with the FEL quirks/uses etc.
I am sure others will have differing opinions.