opentype

It will just merge the entries. Instead of seeing 5 different replies for one topic, there will be one entry for that topic. 

Sorting is only available with the listing templates, not with those frontpage/article views. One could however create listing templates that look like those frontpage/article views. 

New topics are highlighted in contrast to “just replies”. Like this:

Is that what you are seeing? Doesn’t look like “almost double” to me. 

Sure. 
First, create an image attachment in the editor by choosing the file from your hard drive. then click on it, so the image is added to the post content. Then double-click on the image. In the dialog box, replace the content of the URL field with your target URL.   

Yes. 
Or use a third-party solution. 

What have you selected here in the database settings?

 

The initiation method isn’t the most important part. The optimization methods apply to all of them. 
Looking at the screenshots, your system mails go out directly from your server. So you need to make sure your DNS settings are optimized for that as well, not just for the external services like ConvertKit you use. In fact, it could be that adding DNS settings for those external service actually deligitimized sending mails from your own server. You need to make sure that all sending options are included in your DNS settings. 
You can check with your host. They probably have settings and information directly relating to SPF/DKIM/DMARC …
I always optimize this stuff using the Mail Tester website. By the way: You can do 3 tests for free per day. You should end up with at least of score of 9. 

From last Sunday: https://invisioncommunity.com/forums/topic/477126-image-compression/
I’m not sure what else you mean with “automatic resizing” when you apparently don’t mean maximum max pixel size settings. That resizes an images when it is too large. What else do you want to happen?

There is no physical products section. It’s just “products”, with an option to be physical or not. Long story short: those product subscriptions are not going away at this time. 

A checkbox allows for “0” and “1” and “0” is technically a valid choice. 
By the way: the “Checkbox Set” field does work as you request it here, even if there is just one choice given. In this case, it’s “at least one field must be checked”. I use this option to create a mandatory license agreement in one of my stores. 

Database settings:

“Publish Date” instead of “Last Update Date”. 

https://www.sosinvision.com.br/index.php?/file/263-validating-force-user-to-change-email-address/

You have to piece this information together by going through the various parts of the statistics area.
On some pages you can set the date range to “last year”, which will essentially show you what was going on this year if you open this page at the end of the year. 
Some areas can only do monthly views as the longest period, so you would have to calculate the result over the year yourself. 

Where? 
Your hosting usually comes with email sending capabilities initiated through PHP. Does that not work? 

“clear system caches” in the support section usually helps for problems like that. 

Yes. You probably don’t see it because you are looking at your own records, which you can’t react to. 

Just for the sake of completeness: the official solution is …
Turn on “Moderate new records” in the database settings Assign an “author group” to the users Change the database permissions to allow “add record” for this group

Check for template calls in places like Listing template → categoryHeader. 
It will indeed call a stock template for categoryRow there by default. But you can change that to call your custom template groups. 
There might be more places like that. In general, you want to make sure that all {template… calls point to your custom templates. 

It’s usually faulty html in one of the blocks. Impossible to say where exactly from just a screenshot. Could be ad code, theming issues,  user-group styling or even individual forum topics with problematic code. 
I would first try to login as that user to see if you can replicate it. If yes, you can investigate it directly. If not, it might also be a problem on the user’s site. Like ad-blockers interfering with the page and things like that. 

Moving between categories is an admin option both on the front- and the back-end. You just click “move”. 
Changing the publishing date depends on the field “publishing date” being activated in the field settings. 

There is a Deleted Content section in the ModCP to do this. 
However, it only works if the “Permanently delete content” setting in the ACP ist not set to “immediately”. 

There is also the "hide" options as well as the "require approval" option for pages databases. Both options would allow admins to review and work on articles while they remain offline. 

You can add meta tags using the meta tag editor. That works globally, not just for custom pages. 
Regarding <head> content, you can choose to use the suite wrapper or not (see the option in your screenshot). If you do, you use the <head> from the suite without changes, if you turn that off, you can and have to create your own <head>. 

A template redirect looks like this:
{{\IPS\Output::i()->redirect('https://server.com/something.htm');}}  

I think the topic itself doesn’t “know” anything about the Pages connection. That connection is stored in the table of the cms database. So you have to use a manual query to check if the current topic ID is present across any of your cms databases. Might not be a good idea.