Using meta (and link) elements for Microdata is fine. Sometimes there is even no sensible alternative to it, e.g., if specific codes have to be provided where it would make no sense to show them to your users.

Google even uses meta in some of their Rich Snippets examples:

• Products and Software Apps:

    <meta itemprop="priceCurrency" content="USD" />
  

• Reviews:

    <meta itemprop="datePublished" content="2006-05-04">
    <meta itemprop="bestRating" content="10"/>
    <meta itemprop="worstRating" content="1"/>
  

• Videos:

    <meta itemprop="uploadDate" content="2015-02-05T08:00:00+08:00"/>
    <meta itemprop="duration" content="PT1M33S" />
    <meta itemprop="interactionCount" content="2347" />
  

• Articles:

    <meta itemprop="datePublished" content="2015-02-05T08:00:00+08:00"/>
  

So the question is, how much is too much (if there is a limit at all)? And I think it’s safe to assume that there is no hard limit, it most likely depends on various additional factors.

However, it would make sense for Google not to dismiss Microdata markup if only meta/link is used. Why? Because they also support (and sometimes even recommend) JSON-LD for providing Schema.org data, and this consists only of "hidden" content (namely, a hidden script element used as data block).

And this would be what I’d suggest in your case: If you don’t want to add the structured data by marking up your existing elements, use JSON-LD.

Using meta (and link) elements for Microdata is fine. Sometimes there is even no sensible alternative to it, e.g., if specific codes have to be provided where it would make no sense to show them to your users.

Google even uses meta in some of their Rich Snippets examples:

• Products and Software Apps:

    <meta itemprop="priceCurrency" content="USD" />
  

• Reviews:

    <meta itemprop="datePublished" content="2006-05-04">
    <meta itemprop="bestRating" content="10"/>
    <meta itemprop="worstRating" content="1"/>
  

• Videos:

    <meta itemprop="uploadDate" content="2015-02-05T08:00:00+08:00"/>
    <meta itemprop="duration" content="PT1M33S" />
    <meta itemprop="interactionCount" content="2347" />
  

• Articles:

    <meta itemprop="datePublished" content="2015-02-05T08:00:00+08:00"/>
  

So the question is, how much is too much (if there is a limit at all)? And I think it’s safe to assume that there is no hard limit, it most likely depends on various additional factors.

However, it would make sense for Google not to dismiss Microdata markup if only meta/link is used. Why? Because they also support (and sometimes even recommend) JSON-LD for providing Schema.org data, and this consists only of "hidden" content (namely, a hidden script element used as data block).

And this would be what I’d suggest in your case: If you don’t want to add the structured data by marking up your existing elements, use JSON-LD.