Sugar Apple

use software called XAMPP, it will make a webserver on your computer

yes, its possible. WP has user group permission system, you need a plugin to use this easily.

for upload system, i dont any idea about this. maybe a plugin could do this

you`re welcome. good luck

if you`re using cpanel, you can check your “error log”.

‘1193M Used’ that`s so much. just for a wordpress?

actually there are many methode to insert banner (or ads) so, it means many methode too to remove them.

you need control panel access (we talked about wordpress admin dashboard) to remove or change them.

i think its your host problems, contact them.
what do you mean about “changing wordpress sites”?

i am pretty familiar with wordpress. i`ve a blog with over 300 pageviews/day

your site looks normal, i`m not getting 500 internal server error.

how often you get “500 internal server error” ?

500 internal error pages could be occured by many things. could you share your site link?

when this problems start to appear?

i think its .htaccess error

check your permalinks

use modernizr, but wont make it 100% compatible with new wp

i`ve take a look at your site and found, yeah its redirected to youtube after few seconds.
and there`s no strange code in you site. you need to check your wordpress installation but not limited to theme and plugins.

good luck.

until now, no way to add news theme to wordpress.com host,
my advice, find a good host and install your own wordpress.

wordpress.com is pure free wp host, so there will be some limitations.