Multiple questions on DSLRs..?

Please spare me the snobbish attitude we so often see on this category. Yes I'm a beginner and yes some of my questions are perhaps slightly silly to you. Be patient and helpful or don't answer at all if you like. Anyways moving right on! I have a Canon Rebel xs and I have had this one for about 5 months... show more Please spare me the snobbish attitude we so often see on this category. Yes I'm a beginner and yes some of my questions are perhaps slightly silly to you. Be patient and helpful or don't answer at all if you like. Anyways moving right on!

I have a Canon Rebel xs and I have had this one for about 5 months and am currently still learning many new things all the time. I research online, read my manual ask friends etc but there are a few things I am still unclear about:

-I have a 18-55 lens only. What's the next step and best for further away shots such as landscape?
-Is a filter necessary and which do you think is most useful for portraits, nature etc. Everything really..
-I don't understand the live view concept. I go to custom functions and know how to set it of course but there is nothing on my screen as other people have explained it showing so. Am I missing something here?
-What is the best way to take photos at an aquarium? Which ISO speed would you think?
-Is a lens hood necessary or only if one takes many photos in direct sunlight?
-I know it's an age old question but the Nikon D3000 often compared as a low cost dslr along with Canon rebels, it appears to me photos taken by those are clearer?

Any answers would be so appreciated. Thank you for reading. :)
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