Thanks twerppoet for your feedback. I have not received the Ipad yet, but should arrive soon, it'll be my first iOS device ever, since I use Windows.
I will be reading ebooks mostly in PDF, Djvu, Epub and Mobi formats. I was told "GoodReader" to be the best app for PDF reading. I found "DjVu Reader Pro", "KyBook" and "PocketBook" all with good reviews.
As for the keyboard, would this
bluetooth keyboard make it?
Also, is the Ipad secure enough to do online banking and shopping? I mean, is there a need for a firewal/antivirus?
I found out that iOS does not allow to use a mouse, what about keyboard touchpads? are they compatible?
Regarding file transfer, other than wifi, can I use the lightning to USB3 camera adapter to transfer files via pen drives?
Can apps be installed with installer files or am I forced to use the Apple Store?
I like GoodReader because it has a lot of oddball tools hidden away. You can often do things with files that other apps and iOS can't. However, as iOS improves I've used GoodReader less and less. As a PDF reader and annotation app, it's only so so. In my experience it handles realy huge files better than most, and there are plenty of tools, but I don't like the UI as well as Documents.
iBooks is an excelent epub reader. Amazon's Kindle app can import mobi files. I've never even heard of most the other apps you mention, so I can't comment on how well they work.
I don't know anything about the keyboard you linked to; however my experience with flat portable keyboards is that they are fine for typing on the go, but not great for typing a lot. If you expect to do a lot of typing at a desk, you can't beat a good desktop bluetooth keyboard. Apple's keyboards are pretty good, though hardly the cheapest.
There is no anti-virus or filewall software for iOS. Viruses and other malware are rare, and almost impossible to get as long as you stick to the App Store. However the iPad is no more immune to scams, web based scare-ware, and other attacks that involve tricking the user than any other computer. So don't go clicking on shady links like you're bullet proof.
Also, iOS is just a vulnerable man-in-the-middle and other network skimming practices. Don't do banking or other risky stuff on a public network unless you use a VPN.
No mice. No touch pads. Keyboards and the Apple Pencil are pretty much it. Keep in mind that the iOS UI is designed for touch, so a mouse pointer would be of limited use even if you could use it.
The camera adaptor is good only for importing photos and videos. Don't count on it for transfering other file types. Most of us use DropBox and/or other cloud services to get files on/off the iPad. There are a few devices and apps that can work around this limitation, but not Apples'.
Most apps that need to import/export files offer cloud support from various services and/or local wi-fi transfer to/from a computer. Hardware transfer using the USB to Lighning cable can be done via iTunes on a computer, but it's clumsy. Few use it.
To install apps from outside the App Store you need to jailbreak (similar to rooting an Android device). There is some increased risk of malware if you do this, but it's mostly moot at this time anyway. There is no jailbreak availabvle for the current version of iOS. Also, there is less reason to do so these days. There never were a huge number of apps available in the 'safe' jailbreak store (Cydia), and almost all the features that inspired jailbreaking have been added to iOS over time.
Well, that's my oppinion, but I never bothered to jailbreak. Those that did, or still do, are likely to disagree.