1) The newly inserted id is automatically stored in the session and can be passed to the page in the url as well if necessary.
2) You can do whatever design you want if it is intuative.... how many pages you use to create the user experience you want to support should be relative. Two separate forms on the same page behave no differently than two separate forms on different pages, so there is no reason why anything wouldn't work simply because it is on the same page as something else.