Which theme?

Hi all
As a moderately computer literate newbie I would really appreciate some advice.

I want to start a blog with a member signup for visitors to comment. I will also need a facility to run polls rating ideas. This feature should collate the results of the poll.

Ultimately an e commerce facility will be needed.

I am presuming most of these features will be available as plugins/widgets etc.

My question is, when selecting a theme is compatibility with all these requirements an issue or will any theme allow this functionality?

I like the look of customizr but really just need robust reliable easy to learn/use theme.

Could anyone recommend some themes? Also is mobile compatibility available on any themes?

My thanks