If you get time out, you need to contact your host to increase couple PHP parameters like max_execution_time, upload_max_filesize or post_max_size. The default setup are different for every host.
About Paypal, it work too. You don't have to post any question. Just search the forum, there are a lot already. Last time I had problem was with Paypal itself. It solved after I contact Paypal.
Don't use Zen Cart, you will be sorry.