Please I need advice and suggestions

Hello everyone.
We need your advice and suggestions. We operate an E-commerce website called and we are facing some issues with our Website, Theme and the Marketplace.

When Sellers list their products, we are unable to approve before it goes to the front end which is not suppose to be. Also when an order is place Buyers do not receive confirmation email and our site is not as fast as it should be.

We need advice and suggestions for the purchase of the following:
(1) A Marketplace with support that is easy to access and used by us and the sellers, where we will be able to approve listing before they appear on the front end.
(2) A plugin with support that can increase the speed of our website
(3) An easy to use Template with support where we and the buyers will be ale to receive confirmation message when an order is placed, and also one with sharp images.