iamdavehart

the mailto link protocol accepts subject, cc, bcc and body parameters. in addition according to the mailto protocol specification you don't have to provide an address. it works without one, so you can just add a link in the button that has a link like this (%20 is an encoded space, you have "percent encode" your values. you can use an online encoder for that if you want).
mailto:?subject=Hello&body=Hello%20World! if you do it via the link editor in squarespace it doesn't seem to like it without an email (as you've found out), so I'd just type it in manually. Does seem to cause some odd behaviour with the editor though, sqs probably require one so it breaks some of their validation. it does work though!
 

Squarespace stores the settings in a data-props attribute, and it seems that if you can get to that and update it then the timer for the slideshow does appear to honour it. It's possible that there's a race-condition going on here, but I've tested it and it worked on my 7.1.
You'd need business/premium to do it because we're changing an attribute with javascript. put this in the page header code injection (Advanced in the pages Settings):
<script> document.addEventListener("DOMContentLoaded",function () { const slide = document.querySelector(".gallery-fullscreen-slideshow"); const att = slide.getAttribute("data-props"); const attJSON = JSON.parse(att); attJSON["slideDurationMs"]=20000; slide.setAttribute("data-props",JSON.stringify(attJSON)); }); </script> waits for the document to load all its content finds the first fullscreen gallery slideshow in the page gets its data-props attribute and changes the sub-property of slide duration (in milliseconds, so 20seconds = 20000) update the attribute Give it a try!

you could do it in a code block. add a code block and use the following HTML / Style
<div style="background-color:#CB4342; color:white; font-weight:bold; padding:0.5rem 1.5rem; border-radius:4px; display:inline-block; font-size:large;"> STEP 1 </div> if you're going to use this in more than one place, then add the style bit as a class to the Custom CSS in your site (go to Design from the main menu of the editor) like this
.redLabel { background-color:#CB4342; color:white; font-weight:bold; padding:0.5rem 1.5rem; border-radius:4px; display:inline-block; font-size:large; } and then in your code blocks use this class like this
<div class="redLabel">Step 1</div>  
 

the portfolio / project grid has its own padding. so you'd need to remove that by setting it to 0. 
.tweak-portfolio-grid-overlay-height-custom .portfolio-grid-overlay { padding-top: 0 !important; } add this to your page, either within the sites custom css or inside a code block (you would need to put the code above between <style></style> tags if you do that)