You can edit one scene at a time within a single project - setting the WorkAreaBar to cover an individual scene will limit preview rendering to that scene. Once satisfied with a particular scene you can Share it to a separate file if you want to reuse them in other projects - use the WorkAreaBar to cover the range you wish to export. Use the DV-AVI format to maintain quality. Or if you don't mind adding additional codecs add the Lagarith Lossless Video Codec. Bill Hunt has written a Tips & Tricks article on using this.
This FAQ entry will also be helpful: How can I use footage from one project in another?
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What format and resolution of video are you working for? Are you going to ultimately output a DVD or a BluRay disc?
Different resolutions use different workflows.
Welcome to the forum.
As Neale mentions, I like either the Lagarith Lossless, or UT Lossless CODEC's ( Exported/Shared to an MS-AVI - not a DV-AVI). This ARTICLE goes into more detail.
If I am doing an SD Project, and will only be doing a single trip to the editing program, I just stick with DV-AVI. Though compressed, it is only slightly so.
If you have an HD Project, then for ultimate quality, the Lagarith, or UT Lossless, should work just fine.