Go to the Google play store (the icon with a coloured triangle on a white bag) and search from there

You may need to register a Google account unless you already did. You can use your e-mail account.

Yes, there's a (paid) app for Alamy releases:
https://play.google.com/store/search?q=alamy&c=apps

I couldn't find a Shutterstock app but if you visit the usual contributor page at http://submit.shutterstock.com there's a nice mobile version of the site

(I have a new Android smartphone with Gingerbread as well. And using it just to connect to the internet, still not as a mobile! not using a mobile is a way of life)

"which pre-loaded apps I need to keep and which to remove"

You'll find out that it's not easy to remove some pre-installed apps.
The only way to gain complete control over the thing is to "root" it. Which is not illegal, but may void the warranty and even "brick" the phone if something goes wrong. I did it anyway and all went well.

I also installed an antivirus (AVG is free). Viruses on Android are probably less frequent than on Windows, but I'd rather not take the risk.

Besides e-mail, "Whatsapp" is a very useful app for free messaging.

And "Dropbox" to synch files with my computer at home.

And I also find local transport apps useful (national rail, tube, buses...).

But the whole "export/share/send" thing instead of proper "open/save" menus is dreadful: I never know where my files are.