I'm not really clear on how specific sub-domains links and search engine rankings impact the my other sub-domains links and search engine rankings.

If one sub-domain gets indexed does that mean it is likely that the other sub-domains will be indexed as well?

Does a high PR link to one sub-domain benefit and boost the search engine rankings on the other sub-domains or is there no impact?

As far as effecting search engine rankings, if I have a chance to place a link on a non-niche specific site, is it better to use my regular domain name as a link or a sub-domains, or does it matter?

In the same scenario, does any link (main domain or sub-domain) on another site give me all the search engine benefit possible or am I better served having specific links to every single sub-domain on my site?

Thanks again for your help.

Each sub domain is an independent entity. What happens in linking to one will not affect the other(s)

Thanks Chris, that's really helpful.

Typically what does one do as far as content of the index page? Do they just put links to the various sub-domains?

I don't see there is a "typical" scenario. It will depend completely how or for what you are using sub-domains.