1. This depends. Does the one site/business have multiple locations? If it does I link to the location page. Only one location? Then just the home page.
2. Build out a Google business site. In the info section where you can type as many characters as you want, include your CID link, shortened GMB g.page link, and maybe a link to the address's Google URL in this section. You can pretty much abuse your GMB site with PBN links. I also like to create exact match domains, blast em with PBN links, and 301 to the GMB site.
3. Not sure what you're asking here. Are you saying make your website link the GMB link? Which GMB link? Many people do use the Google business site here, but I advise using the actual site URL where you have more control over the data/content.
4. It is but I'm looking for someone good at the moment.
5. Create your own reviews. Get aged gmail accounts from the US (or your area), warm them up by reviewing other businesses, watching Youtube videos, browsing Google, and just use the accounts like a regular person. Change your location in Google with Command+Option+i > More tools > Sensors (on mac, not sure for PC) to pull up the sensors and change your long/lat.
