Hi,

Here are some tips that come to my mind.

"we will need a simple template for businesses to write something on their profile, with options to add upload photos and include google maps"
>> I would suggest modifying the profile page that is already included in the core of concrete5. With some custom attributes this can be done quite easily.
>> For showing the users each profile I would either build a custom block or a static single page that would print out the details as you want to.
>> Here's some tutorial of single pages if you're not yet familiar with them:
http://www.concrete5.org/documentation/developers/pages/single-page...

"Then customers can write a review/add a testimonial with a ratting of 1-5 stars."
>> This can probably be achieved (at least with some modifications) to this add-on:
http://www.concrete5.org/marketplace/addons/ajax-star-rating/...

"This will require:
 
user registration system incl. area where users can log-in and update 
their details as well as upload content
"
>> These are in core concrete5.

"people need to be able to search by location and search for businesses"
>> As said, this can probably be achieved with custom user attributes. If you need more detailed location search, I would probably check this add-on:
http://www.concrete5.org/marketplace/addons/dealer-locator/...

"Also will have paid advertisement from businesses next to search result, and other places"
>> Again, few options here:
1. The concrete5 add-on for ad server:
http://www.concrete5.org/marketplace/addons/advertisement/...
2. Setup your own ad server (e.g. openx) and integrate it to your site. This can be more trickier than the first option but with high traffic sites might be better to share the load to multiple servers.

"Also need space on each users account so customers can post a review with a ranking from 1-5 Star."
>> There's an add-on for this:
http://www.concrete5.org/marketplace/addons/reviews/...

"This means we need site administration - where we can manage registered users and ensure no rude language is used from customers writing their comments."
>> You can achieve this with the user grouping system included in core concrete5. Just add some group for site admins and give them special rights to monitor the activities and delete posts etc. Might also be worth to check out advanced permissions:
http://www.concrete5.org/documentation/general-topics/simple-permis... (scroll down to advanced permissions)

I am not really sure where to start, and help on themes to use etc would be a big help with this.
>> There are quite good instructions available at this site by just using the search. Some search words that you will most definitively need are "single pages", "permissions" and "themes"
For basic theming, there is this guide:
http://www.concrete5.org/documentation/developers/pages/themes/...

If you want some of your single pages to use a file from your theme, you should check out the config/site_theme_paths.php file, it already has some comments to help you further.


Br,
Antti / Mainio