I am about to role legendary for Speechcraft. I will then loose the perk I got to invest $500 into business. Will those shop owners remember I once invested in them or must I do it all over again?

Not 100% sure on speech but i know on all other skill trees you lose everything, minus the perk points you get back. Im pretty sure speech is no different.

Try it and see. Save before you Legendary your Speech in front of a vendor you've invested in, then check their Gold afterwards. Just be sure to let us know what happens.

When I did this I lost the perks for selling anything to anyone...the everybodys a fence...the more cash from opposite six vendors.........BUT!

I noticed that I still have the extra 500 and extra 1000 coins per vendor!!!

I, too am interested in how your game deals with the effects of going legendary on Speech.