You can add this CSS code the review template custom CSS setting...

img.wprevpro_t1_IMG_4 {
width: 100px;
height: 100px;
}

After you have the reviews on the Review List, go to the Templates tab and create a new review template. After you create it, it will give you some instructions to put it on your site.

There isn't an option for that at the moment. This app is currently only for displaying reviews from the 3 sites you mentioned.

What is the Yelp URL you are using?

Are you talking about Facebook pages? Please provide more details.

Really the only way to make it smaller is to control the font size. Add this CSS to the custom CSS for the review template in the app. It will also take off the all capitals in the reviewer name.

.wprevpro {
font-size: 13px;
}
.wprevpro_t1_SPAN_5 {
text-transform: none !important;
}

What is you home page URL? Did you put the code or add the section to your home page? Do you have reviews downloaded in to the app?