HVAC replacement and mold

I’m not sure where to post this one, but I’m so stressed and needed to vent. Our house was built in 86 and the heat and AC system has never been replaced. This week i noticed a musty smell coming from the air vent. I had someone come out and when he opened up the system we could see there was some mold growing all around it.

Although mold had always worried me, I’ve calmed myself down about it over the years with research saying it’s really not as scary as we often make it out to be. There’s no sign of mold anywhere else in our house or even near the unit, just inside it.

So, we decided to replace the whole thing. It’s a huge purchase, so expensive. But we’ve needed to do it for a long time and this was the final straw. But my anxiety is so high! They are coming tomorrow to do it, so the turn around was immediate. I worried that maybe we should have our air ducts cleaned first in case there’s mold in there and then it gets into the new system. They told me this wasn’t a worry and if the smell isn’t gone we’d figure out next steps - maybe then considering duct cleaning.

I think this makes sense but for some reason I’m just so so anxious about the whole thing. I get irrationally anxious any time we have to have home projects because I hate when they cut open walls or remove stuff because I feel like dust and maybe mold in this case is going to get all brushed up and get all over the house.

We’re using a really reputable company and I know they’re experts. It’s just a lot all of the sudden!!