Marc

It looks like when you downloaded, you didnt so select to include the converters. You need to ensure you have, as you havent got the latest files for that application

You can choose to disallow registation from set email domains by using ban settings. Go to Members>Member Settings>Ban settings, and set them up there. 
For example, if you want to block everything from gmail you would add *.gmail.com 

There is no way in which to downgrade the software. The only way in which to do that would be to restore your site to the backup taken before you did the upgrade

There are a few things that google apis may be used for. Things like maps, ip lookup and many other things. Google is also contacted for other things such as fonts. You can't switch all of these off. You would need to correct the issue with your hosting company

It is very much likely to be what Sonya mentioned above. You would need to use different images, or change your theme to suit

I have created a ticket on your behalf, and we can get that sorted out for you. I will be in contact shortly

That has now been resolved for you. Noticed you were also having cache issues on the front end and showing CSS, so have resolved that for you while I was there.

Clubs comes with core. However you only get the ability to add items on those clubs related to the applications you have purchased. For example, if you dont have forums, you cant add a forum to a club

It depends on whether they have stored their card details when they entered them the first time. If they have, payment would automatically be taken.
The user would leave the club if they no longer wish to pay that subscription

You can of course. If you take a look at the following guide, this shows you how you can add any reactions you would like to add
 

Just an update to this, anyone updating to 8.1 will now be notified there could be issues, until such point as we provide support for that version

You are indeed correct in the 2 applications you would need to purchase in order to have those 2 items. 

I believe the question there is more whether you can search for the club itself? If so, there is no facility for this at the present time.,

You would likely need considerable custom coding for this. It wouldnt be a simple template change. In order to develop for the platform you would need coding knowledge. Our guides for developing with our plugin and application system can then be found here
https://invisioncommunity.com/developers/
With regards where you can find help to do this, there are 3rd party developers who advertise their services in our provider area. You can find this in the following location
https://invisioncommunity.com/third-party/providers/

Then indeed, you would use "clear cache" which can be found by logging into your admin CP, then clicking support in the top right. 
Note there are some guest caches server side, which may well take a few minutes to clear

the word "the" is a mysql stop words and woud not be included in search results. That and the default minimum 4 letters for mysql fulltext searchign means items such as the above would not really be searchable in that manner unfortunately. 

You could use the following recovery method to try and disable the item
https://invisioncommunity.com/4guides/client-services/getting-support-r292/#recoverymode

Unfortunately the issue there is within your custom theme. The issue is quite likely in your edited responsive.css template.

I see this has now been done for you. Please let us know if you require any further assistance. 

You need to update your site to use ssl first of all. You can update to https using the method described here, if you have a certificate applied on your server
 
Once you have done that, you would need to ensure you change the callback URL as mentioned above

sitemap will not update instantly. It usually does so once a day. It looks like items have only just been created there

You would either create the account first then change the details if you wish by editing the profile data section, or just leave it and it will prompt the user on first sign in that they need to complete that item

There is no way in which to disable the available update flag if there is an update available on the update location set by the author. You would need to contact the author for a custom version of that product that does not point to the update

There is no way in which to export a full forum in that manner. The only way in which to keep it locally would be to create a full copy of your site

Just checking  a few there, they are indeed showing the "mark as solution" option. Note that you would only see this if you have the moderator permission to mark any item as a solution, or you are the topic owner