both questions are already answered in forums, I think.
1. dns: for editing a single domain, just use link "edit dns template" after adding your domain. for changing/setting ns1, ns2, for all your domains (existing and newly added) edit dnszonetemplate file in ehcp dir. after changing that file, use ehcp->options->sync dns

2. for assinging some ip's to some domains, follow (step by step):
a) ehcp home->easy add domain
b) bottom links (Similar/Related domain Functions, Different IP(in this server, not multiserver) -> Easy Add Domain to different IP
c) once: list/add server IPs -> add IP to this server (the IP must already be configured in ubuntu server, at system level; ehcp does not play with/change server IP's actually) ; return to step a

d) select IP and add/setup your new domain in that IP

this should work, I did not test it soonly, in past, we had tested it.

nice to see you in ehcp community

1.
use {dnsip} to use your normal server ip, that is defined in options.
to use a different ip, or your second ip, use directly ip.
that is, this should work:

ns1.crowarez.com. IN A {dnsip}
ns2.crowarez.com. IN A 205.204.20.23

this should work also:

ns1.crowarez.com. IN A 205.204.20.22
ns2.crowarez.com. IN A 205.204.20.23

in ehcp templates, tags that are enclosed in {} are replaced by ehcp code by its actual values, if any.

so, {dnsip} maps to your dns server (nameserver) ip, or simply your server ip where a single server is used for all needs, dns, webserver, mysql etc.

{webip} is for webserver ip, or simply your server ip.

{dnsip} and {webip} is used separately because ehcp supports separate dns/web/mysql servers, mostly.

2.
"If I already have a domain added in EHCP how can give one IP for this domain" => No gui in ehcp for this, you can do this (manual) way:

go to mysql/phpmyadmin, ehcp db, domains table, edit your related domain, fill "webserverips" with your desired ip,
then, ehcp gui->options->sync domains

this should work.

For making this in gui, I may accept this as a "feature request". It would be better if you make a "feature request" in https://launchpad.net/ehcp , blueprints section, so that this will be public and known to everybody, and maybe people say their opinions, get used to use official project management tools of launchpad.

* Normally in ehcp (and above description), Assinging an IP to a domain does not mean that domain will open in browser when you go to http://thatip
Assigning means, that IP is reserved for that domain, for serving pages, this has some advantages like speed, ssl etc.

"when someone types in a web browser 205.204.20.22 that it opens www.myweb.com" => To do this, you need to edit apache configs. no gui/direct/easy way in ehcp. Sory about this. there may be some posts in ehcp.net forums describing this. I am not sure. I (or somebody) may write a howto about this later.