Scribus is - as far as I'm able to tell - totally memory-resident when it's running. This means that you need enough memory to hold all of the resources - the SLA file itself, fonts, images, etc. - that the document you're working on is using (as well as the OS itself, Scribus, and any other software you're running of course).
The amount of memory - both physical RAM and virtual memory - that you actually need is more dependant on which OS you're using than most people realise. Windows, historically, needs more memory to run happily than OSX does, and with Linux it really depends on the distro. This also changes depending on whether you're using a 32bit or 64bit OS version. (This is a big simplification but it's a useful rule-of-thumb.) For example, Windows 10 needs a minimum of 1GB RAM on 32bit and a minimum of 2GB RAM for 64bit whereas OSX El Capitan needs 2GB minimum but its memory management is much better than with Windows so it can run quite happily with 2GB while Windows will usually struggle quite a bit. And these are absolute minimums that the OS can comfortably work within for basic functions. Basically you can take that minimum off the amount of RAM you have and what's left is "usable" RAM. (Again, a big simplification.)
One thing you could do would be to use the Scribus "Collect For Output" function (not compressed) and look at the size of the folder that is created. (The collected output is everything that someone would need to re-create the document and therefore will give you an idea of the total size of all of the resources.) If the folder size is less than the amount of physical "usable" RAM that you have then you should be absolutely fine (unless you have done something weird with your virtual memory settings). On the other hand, if the folder size is way more than twice the size of your "usable" RAM then you might want to look at getting more RAM. Otherwise your machine will be page swapping memory between RAM and disk (virtual memory) far more than you might want it to (and it could be causing other problems).
With specific mention to the problems you're having, you would need to be much more detailed when explaining what's happening before anyone could diagnose what's going on.
For example: By way of explanation, for "Hangs sometimes (Text Frame) after calling up Properties window.":
1. What do you mean by "hang"? Exactly what "hangs"? Does the "hang" end or do you need to restart something?
2. What do you mean by "sometimes"? Is it frequent or is there a pattern depending on use or document size/type?
3. What does "(Text Frame)" mean in this context? Are you clicking on a text frame? Are you moving a text frame? Are you right-clicking on a text frame? Are you trying to edit a text frame? Are you changing a text frame's properties etc. etc.
4. Why are you "calling up" the Properties Palette. It's way more usual to have this open all of the time. The general recommendation is never to close it unless you want to deliberately make more work for yourself.
Apologies if the above might sound picky but its very difficult to diagnose problems without knowing exactly what's going on and in what context. If you can supply more information then someone might be able to help further.