I need help to choose right wordpress theme.

Hello,

I need right theme for redesign my existing website.

Currently site running on wrodpress. But current theme cant do some things for me.

First I need FAST theme with good design. Speed in important.
That theme needs to be modern in technical requirements.
With good support.
To be responsive.
E-commerce allowed.
Newsletter. (not necessary)
Donation. (not necessary)
Also to many plugins not good.

Site current offers free graphic resources for download. I use plugin “download manager” for managing files.
I don’t have blog now but after redesign I need blog also. But like separate link on website in main menu.
Also don’t need blog on first page just on single “blog” page.

But biggest problem is file managing. I wondering does any of themes support file managing like plug in who I currently using? And does that plugin good?

I’m not geek and need professional opinion what theme to purchase.
I look theme on themeforst but cant decide what is right chose…

Redesign needs to be right chose.

Thank you.