How worried should I be about these warnings? How do I go about changing the style sheet for border attribute and headings? Help is much appreicated - loving this template

TheLine 596, Column 277: The border attribute is obsolete. Consider specifying img { border: 0; } in CSS instead.
…html" width="728" height="90" border="0" alt="Sheds.co.uk Leaderboard 1" /></a>

Warning Line 589, Column 71: Section lacks heading. Consider using h2-h6 elements to add identifying headings to all sections.
…/nav> <section id="yt_spotlight1" class="block"> <div class="container">



Line 2355, Column 102: Element link is missing required attribute property.
…s.mailchimp.com/embedcode/classic-081711.css" rel="stylesheet" type="text/css">
Attributes for element link:
Global attributes
href
crossorigin
rel
media
hreflang
type
sizes
Also, the title attribute has special semantics on this element.


Line 2356, Column 23: Element style not allowed as child of element div in this context. (Suppressing further errors from this subtree.)
<style type="text/css">
Contexts in which element style may be used:
If the scoped attribute is absent: where metadata content is expected.
If the scoped attribute is absent: in a noscript element that is a child of a head element.
If the scoped attribute is present: where flow content is expected, but before any other flow content other than inter-element whitespace and style elements, and not as the child of an element whose content model is transparent.
Content model for element div:
Flow content.


Line 2367, Column 8: Stray end tag label.
</label>


Line 2581, Column 110: The width attribute on the table element is obsolete. Use CSS instead.
…tyle="width:100%;"><table width="100%"><tr><td colspan="2"><div id="cookieMess…


Line 2581, Column 130: Table column 2 established by element td has no cells beginning in it.
…table width="100%"><tr><td colspan="2"><div id="cookieMessageText" style="padd…

OK, so my previous message wasn't a hit but how about these warning on Bing and Google webtools:

The <h1> tag is missing.
The <img> tag does not have an ALT attribute defined.

The H1 tag is critical, so how do I add it to the style