SnazzyView

Yes and no, you could achieve it with CSS but you would need to set the name field to make it not mandatory. If you would like to do this just enter the below into your websites global CSS.

.last-name {
  display:none;
}

But if you want to just collect somebody's first name then I would just recommend using the text field instead and just calling it first name.

https://support.squarespace.com/hc/en-us/articles/205814018#toc-text

Just based on my experience the feature usually pays for itself and more, then anything else you also get with the Advance Commerce plan is just a bonus. But you will need to have reasonable volumes of online sales though. By virtue of the feature you're recovering revenue that would otherwise be lost, if that revenue generates profits greater than the feature, then it's worth paying for. Plus you're potentialy adding repeat customers, so perhaps you'll also need to take into consideration the lifetime value of your customers. 

I would look at your current analytics and see how many carts are being abandoned and how many are recoverable. I would say a good rule of thumb is if at least 10% of the recoverable carts cover the cost of the Advance Commerce plan then it is worth upgrading. Abandoned cart emails are surprisingly effective so you may find that the recovery rate is greater than 10%.

Of course the effectiveness of your emails will depend on the copy of the emails themselves. But in addition to just recovering carts I've also found them invaluable for users providing feedback. Asking a question, like 'do you need any help' can help optimise your store even further to increase future conversions; like expanding which regions you deliver to or even UI improvements. 

As for third-party software, I can't think of a way that it's really possible. As @brandon says, you can't really get the users email address to send an abandoned cart email.

There's not really an automation feature as such but you can turn a blog post into an email campaign but you have to send it yourself.

https://support.squarespace.com/hc/en-us/articles/360001280668#toc-turn-a-full-blog-post-into-a-campaign

Unfortunately Squarespace are rather secretive around  v7.1 just like they are everything else. For me personally v7.1 can't replace v7 without some big improvements to the header, like you mentioned secondary navigation.

It would be nice to get some sort of direction or even stability from Squarespace regarding what they have planned but we probably won't hear anything until their test is over. But I know that they do plan on supporting v7 for some time to come, they just can't guarantee new features will make it to v7.

Sure, just place the below in your websites global CSS.

.sqs-block-summary-v2, .sqs-gallery-design-carousel-slide {
  padding-bottom:0px!important;
  margin-bottom:0px!important
}

Have you loaded the jQuery library in your code? If not try adding the below to the global code injector header of your website and seeing if it works.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

Unfortunately there is no way to natively do this in Squarespace. If you use Stripe billing then you would completely bypass the Squarespace backend. In addition it would also be harder for subscribers to manage their subscription themselves because they would not be able to login and cancel it themselves. 

No, it’s not possible to edit orders. For fraud reasons I would recommend that you cancel their order and make them place it again with the correct delivery address. In addition if they pay with PayPal and you don’t send to the address on the order and they claim it never arrived then PayPal will automatically refund them.

If the just want to remove one of the products then you can partially refund the order for the value of the item. The item will still be listed on the order but they won’t have to redo the whole order.