Issue with Table of Contents Formatting in eBook on Mac's Books App

The simple answer is that tabs will not preserve in an EPUB export. That's why your page numbers are flush up against the chapter title. That said, I would encourage you to think of an EPUB TOC as a different beast than the print. Does it really need page numbers, for example? As long as it's hyperlinked to the correct location in text, than it's fine. The print page numbers, in this case, might be confusing to the reader. 

The items are blue because they are hyperlinked. That is the default hpyerlink behaviour. You can change that in the CSS but for accessibility reasons, I would encourage you to leave it to the bright blue and underlined default. 

First, the general caveat: EPUB is highly dependent on the reader you choose. Hardly any two will render a book the same way. It's best to test/proof your EPUBs in a plain-vanilla, standards-based reader like Thorium or Calibre. Apple's reader is almost good for this, but has some quirks and "enhancements" that either fail to present an EPUB in a completely standard way, OR are aspects you have to address if your market is Apple/iTunes. (One export won't work well for both, and yet a third is needed for Kindle/KDP, of course.)

What you're seeing probably isn't too reader-dependent, though. Some, yes, as TOCs are basically a list of links and each reader handles links in its own way. (Some allow link visual characteristics to be styled; others present blue text with an underline, old browser styles, no matter what you do.)

You don't say if this is a reflowable EPUB or a fixed-page (FXL) one. FXL is... not recommended except for a very narrow range of books, those that are basically "picture pages" like children's books and graphic novels. If the book is basically text, it's preferable/recommended to export it to reflowable.

TOCs also have to be anchored in place — the text frame, of which there can be only one, needs to be anchored to whatever text it's meant to follow (such as a copyright page/notice). If not anchored, all kinds of odd things will happen, usuall the TOC falling to the end of the document. (Any time an EPUB element ends up at the end... it wasn't anchored in place.) Since you didn't mention that, I am assuming you're exporting to FXL. The bad news there is that very little can be done to restyle or override FXL; you get what you get or you start over, more or less. In reflowable, you can apply ID styles as well as CSS styles to help adjust the TOC a little more to your preference  —but not completely, as the reader controls many aspects.

The solution, really, is not to include an in-text/displayed/inline TOC. They are not needed in e-books and are of use only in highly technical books where a detailed TOC can help organize and locate information. For novels, narratives and basic nonfiction... they add nothing but clutter and headaches. Use a well-defined dynamic TOC instead and let the reader manage it. (Define the TOC in the TOC menu, under a specific name like EPUB or EBOOK); then specify that menu in the EPUB export menu.) A dynamic menu is what e-books should use and what most readers (the human kind) rely on.