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- there are ways. See e.g. Adblock package release for turris omnia
- I’m not certain about some others. You can search the forum, e.g. throttling is certainly discussed in some threads.
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- torrents: there’s e.g. transmission service. It’s common to put such stuff on USB-attached drives.
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- yes, e.g. https://www.turris.cz/doc/en/howto/nas
I have 1GiB. Lots fits into such size, if one doesn’t need to run a browser with modern web. (The fact that Omnia is 32-bit also helps a little.) IMHO 2 GiB is only really utilized if you want some heavy stuff in containers, or perhaps if you want the extra disk cache 
ATM my memory usage (without cache) is around 100 MiB.