WordPress.org

Can I put more than 1 inline post on a page?

Yes.

Does this act recursively by including posts within posts within posts?

No.

What usage do you recommend as best practice for this plugin?

Because of the recursion issue, I only inline post onto pages. Wordpress does not strongly differentiate between posts and pages other than by a post_type flag. This means you could inline a page into a page. Best practice is to only inline posts into pages.

How can I adjust the inline post's appearance

You should be able to fully control your form's appearance using CSS. The HTML output is fully embedded with CSS tags to make personalization easy. The DIV tag is of the form:

<div class="ggis-inlinepost" id="ggis-inlinepost-f56-p69">

The class applies to all inline posts but the id specifically identifies the post inlined (f) with the page it is inlined onto (p).