1) Can't just change it. If you do, all your current content (which uses that class) will disappear. Do this: create a new class which you call "My Article" or something. Make sure it consists of a text line (title) and two text fields (intro and body).
2) The attribute_view_gui function includes the view template for the datatype that was used for that attribute. You could simply change/override this template if you want it to render differently. Even if you extract the XML text directly (not using the view_gui function) eZ publish will probably still insert the p tag (this is a design issue that has been discussed back-and-forth for some time now). The only way to get around it is to pump in some magic CSS.
Two more question:
1. Now the url to my site on local Linux server looks like:
http://ezpublish/index.php/mysite/ When I will finish the development, and will transfer all files and databases to remote server how should I setup the system in order to have http://www.mydomain.com/ url?
2. Also, are there any possible troubles with transfering developed solution from local server to remote?
3. You have developed a GREAT solution, I havecheked about 20 OpneSource CMS, but your is the best one. (I hate *Nuke CMS :). Do you plan to create light version of EZPublish? As it is too big and complex, requires a lot of mem and CPU resources.