Video editing is resource intensive, and a gaming class PC is recommended for lengthy, hi-def or complex projects. Use the 64-bit version.
Your thought is a good one: Save sequence one, restart VP, Clear Unused Cache Files (OPTIONS | DISK tab), then build sequence two. Later, import sequence one. Working on a specific sequence doesn't 'unload' the others.
Another approach, if necessary, is to break up a project into several parts, export each, then import and assemble them for the final export.