opentype

For the background color of the current day:
.cCalendar td.cCalendar_today, .cCalendarWeek div.cCalendar_today { background: #FF0000; } The title of the event over the entire period is set as part of the calendar the event is assigned to. You change it in the ACP in the calendar settings. 

Yes. Type “post before register” in the ACP search bar to quickly get to the setting. 

Nothing to fix. It’s just a newer/longer kind of IP address. 
https://en.wikipedia.org/wiki/IPv6_address

What are the settings for this block? Is it maybe limited to only show featured records from some forums?

Yes, but you have to manually change every instance of the word “club” in all language strings. That’s several pages of language strings. You would also need to customize the club URLs. 
(I wouldn’t really recommend it.)

On the front end, you can drag the Member Statistics widget onto any page. 
In the ACP, there is a similar widget for the Dashboard. 

Use the checkbox in the topic view to select all the posts you want. There is no limit of how many posts can be selected. Once a selection was made, there will be a button bar with possible functions like hide, merge and split.  

The custom fields offered on the database form page depend on permissions and the category they are activated for. So, it that sense, they can be “selected”. I am not sure what you wan on top of that. Maybe give a specific example so it more clear?

ACP → Community → Clubs →  [your club] → Edit → Privacy. 

Not much if your site has an international audience. They are humans who have the sad job of creating these accounts manually. 
The obvious solution would be to not give them anything to fill in after registration (Website, About me links …). But that’s something IPS needs to implement. Discourse solved that through its Trust Level System. Invision Community needs this as well. A new Discourse user cannot:
A huge array of clever spam prevention measures which are slowly and automatically lifted over time when a user proves itself to be an actual member, not a spammer. 

Yes, it’s normal. 
See this recent topic about spammers creating such accounts. 
https://invisioncommunity.com/forums/topic/462206-spam-defense-tuning/
 

That’s exactly how it works. Just paste the URL from YouTube or Vimeo and it will embed. Example:
 
If you really want to deal with the embed code, you can’t just post the code into the editor, as the editor doesn’t process HTML in the text mode. You would need to switch to the source code mode. 

You can just post the image URL, like https://someserver.com/theimage.jpg

The variables are accessible from the widget as $memberCount, $guests, $anonymous, but the idea of the widget is to list the names of the members itself. It’s not about full stats. 
For an alternative view and a turn-key solution, you can also check out this plugin:
 

Put this in the custom.css
.ipsBreadcrumb_bottom { display:none; }  

It’s this value in the theme settings:

Replace the 80 with a higher value. The logo will then be scaled up. 

Yes, it is possible. For Stripe and credit cards, the user gets a checkbox to store the card authorization. For PayPal, there are the so-called Billing Agreements and when you set up the payment method, you choose if that is turned on, off or optional. 

ACP → System → Applications → System → Search → Permissions 

But what would the “fix” be? It’s intentional the way it is. Not every image in a post is suitable to represent the entire topic. 
If you want to assign the first attachment in a post, there is a marketplace file for it. 

It will be right in that area you made a screenshot from if you don’t use categories. If you do use categories, it will be in the settings for the category. 

With an address on file, that part gets skipped during checkout, but users can still click on step 1 again:

And of course, you should add a link to the address section to your menu if you don’t have that already. 
The link will look like /clients/addresses/

It’s expected and usually nothing to worry about when content is deliberately blocked through a robots.txt. But have a look at the URLs it is giving as example and check to make sure that removing them from the index is okay. 

It’s a flaw in how Commerce treats renewals in general. It’s unrelated to your price change. 
 

Pretty sure that’s just a description of this functionality: (activating a CSS file for a specific page)

Create the feed blocks in the ACP and then add them on the front end as Custom Block.
(I prefer that anyway because of the added options like permissions and templates.)