soundfonts

i been trying, for quite some time now, to get and install sound fonts. the manual isn't exactly clear on this so please don't send me links to the manual. i've read through that several times and it only creates more questions than answers.

when I down load a soundfont. some i can decompress and others i can't. the ones i can't because it requires some special/different/non-standard decompression/un-zip program to be installed, i simply move on because that is a big red flag.

the ones i can decompress or un-zip, i'm not quite sure what i should do with the presently installed or default soundfonts that were installed when i originally installed musescore.

particularly, i would like to know:
do i have to remove the old sound font?
what will installing the new sound font do to my existing scores such as: what will this do to the instruments sounds assigned to those existing scores?
what should i expect the instrument menu to look like in the mixer panel if i don't remove the original sound font?
is there a way to separate instruments into sub categories so i don't have this giant list i have to scroll through every time i want to change an instrument?

any help would be appreciated.