I'm very new to using an Android-based tablet as well, so I'm far from being an expert but I might still be able to help you as I've recently had to work out some similar things for myself:
2(b): An app is simply a program on your tablet. It will come with some standard Android ones supplied (probably plus one or two added by Acer). You can download and install others (either free or for a small charge) from the Google Play store:
https://play.google.com/store/apps?utm_source=en-us-ha&utm_medium=ha&utm_term=google+android+apps+market
(You'll see from that link that apps are often more closely linked to a very specific task than Windows programs are, For example, there are apps that let you book rail travel or view newspaper pages, without needing to use a web browser).
1(a) Your tablet will come with an Email app which lets you access most email services. However Gmail is an exception and you need to use a special Gmail app for it. If you use those apps you won't be using webmail (because they function in a roughly similar way to Thunderbird on your PC) but you could still access webmail via your tablet's browser if you so choose.
1(b) You need to check how Thunderbird is configured on your PC. If it's set up to use POP3 email then it's likely that when you download messages they'll be deleted from the server so that they won't then be accessible from your tablet. The solution to that is to go into Thunderbird's settings and look for the option to 'leave mail on server'. If you're using IMAP instead of POP3 there shouldn't be such a problem.
2(a). Google Translate is definitely available as a free app:
https://play.google.com/store/apps/details?id=com.google.android.apps.translate
3. You can definitely change the language settings on your tablet but, because I've never tried it, I can't tell you how easy or difficult it is to toggle between the two. (Incidentally, irrespective of whether you're using a PC or a tablet, you might find this site useful:
http://greek.typeit.org/ ).
4 . . . doesn't seem to be a question!
5(a). Once wifi is activated on your tablet it will automatically scan for all available networks and you can quickly access any that you know the password for (such as your home network) or that don't require a password (such as those in Wetherspoon's pubs). Note that there's a registration and log-in process for places like Wethersppon's but it's very simple. You just try to access any web page and you'll initially be diverted to the log-in page.
5(b) Your tablet will come with the default Android browser, enabling you to access the internet. (BTW. You don't use Bing to access the internet on your PC. You use a browser [Internet Explorer? Firefox? Chrome?] which happens to have a search engine called Bing available as your home page. You could equally well use any other search engine, as you can also do on your tablet). Alternative browsers are also available as free apps.
6. Tablets use a micro USB connection because there simply isn't space for a full-sized one. Your tablet will be supplied with an adapter lea so that, for example, you can plug one end into the tablet and connect the other end to a USB memory stick.