If you're lucky you could seal the holes with white silicone but we had ugly blue tiles and a scratched up tub.

in my rentals that have fireplaces, I seal them completely beside stating in the lease that they are off limits

Sealing is typical for brick/stone foundations so that's easy.

I need to hire someone to seal every single crack or space around the exterior of the house and foundation, that should be beneficial.

I put all new flooring in the upper level of their unit, its a bi-level duplex, and the bedrooms are in the basement, which has carpeting, as did my side, but I tore my carpet out due to years of dog urine never cleaned out of it, which soaked into the cement and even after enzyme cleaning and layers of scent sealing paint and then vinyl plank flooring, I can still smell it in the damp weather.

It needs to be dug outside and basement walls sealed from the outside, then a trench along those walls dug into concrete in your basement with a sump pump installed beneath to pump water out to your back yard or wherever your ground slopes down.  

My wife and I would watch "Flip this House" while we stuffed and sealed and stamped.

I was originally thinking of sealing the whole plaster or cement-like mixture but wasn't too sure about the idea.

We will fix smaller things such as: replacing filters, tightening leaky faucets, and sealing cracks in windows.In addition we will provide 24/7 emergency response services when nightmares happen (think pipes bursting in the middle of the night, furnace going out in the winter months, etc.)We would like to establish a partnership by offering a free month of services with absolutely no obligations.

I would also advise sealing that refrigerator crack so no liquids can enter it since you said it is on the bottom.