R_frick,
Welcome to the Forums!
I'll second the good advice given already, and add this about the fruit: if you are heating your must (in wines and meads it's called must, in beer it's wort), don't add any fruit until the entire batch has cooled down to roughly yeast-pitching temps. Heat will "set" the pectins in the fruit, very possibly lending a troublesome pectin haze to the finished mead which will be very hard, if not impossible, to remove. If you plan to use pectinase, then the temperature issue isn't as important. Many people boil or heat their musts, often with very fine results; keep in mind though that it is not a necessity to do this with mead the way it is with beer -- in fact many people (myself included) feel it tends to be detrimental to the final bouquet and overall profile of the mead. There is no reason, from an infection standpoint, to ever heat a mead must. Honey has natural antibiotic qualities, making it a very safe addition from the start. Healthy fermentations will overrun and outcompete native or airborne microbiota, and the higher alcohol and relatively high acid content of the mead/must adds up to a very hostile environment for all but a few unwanted critters -- and these are rare indeed. If you practice good, basic sanitation techniques, you won't have problems in this regard.
Mead turning into (bad) vinegar can and does happen occasionally, though it's actually rare. I've been doing this for a lot of years, and openly admit my sanitation techniques could use improvement (laziness), yet I've never lost a batch to acetobactor. I've done OTHER bad things to some of them, but we won't go there. The point is, as in beer making, and probably most other things in life -- difficult as it can be sometimes -- the key here is not to worry.
Can you post your exact recipe, just for S & G's? Mango sounds yummy (though I'd go heavier on the fruit -- say five to ten pounds -- and add 2/3's in primary, and the rest in secondary, which will give you a nice ratio of fermented vs. more of a fresh fruit flavor -- but that's just me).
Again, welcome, and keep us posted!
-David