Let me be the first to set your mind to rest. This isn't something that you need to worry about.

Instead of worrying about which one to use for SEO, make your choice based on your development limitations. Posts and Pages have different limitations and built in funcinalities (for Wordpress) but not for SEO. All of that being said, if you can customize, or hire someone to customize your theme for you, there are not any limitations. For example, the home page of our website pulls in excerpts from posts marked "services" and displays them in the "service" section of our home page.

Don't worry about it. The "too many links" message is based on Google's suggestion to have less than 100 links per-page. Obviously site-maps are going to be an exception to this rule, and with good reason. You are fine.