Your 1100 D is a very basic body which is good for people coming straight from Prosumers or Point & Shoots. Use it for some time and when you find that you actually need more controls over the parameters required for different situations its only then you should upgrade the body. I did the same. My first camera was a 600D which is excellent even today but then over a year of using it for birding and late evening ISO focusing FPS issues etc etc made me go for the 7D. Now I feel even 7D ain't good enough but the 5D Mark 3 or upcoming 4. Its never ending.So its totally need and use based requirement.
Now coming to lens. The first zoom I had for birding is my 55-250,I know its laughable but its sweet spot was at 200mm after which it gave distortion of various kinds from barrel to elemental etc etc.But the lens is good and is a very sharp copy. Then I got a 70-300 Tammy which was fast way better focusing and less distortion even that was not enough do I got a Tammy 150-600 excellent lens sharp as hell alls fine till I used my uncles prime 800 from Canon. There's no end to it so get only what you need. And I just don't need that 800mm L prime from Canon coz I'm not pro neither I work for NG nor I will go to Masaimara,so its up to you at the end of the day!
so is it a good slr
