RE: Interim accounts and Nav
Oh dear, that is big beast jobs module :) I don't think I can explain it in a post, as there are so many variation and no 'commonly' used framework, as it very much depends on the industry and the purpose of using costs - whether you use items, resources; costs or just revenue, or maybe just time spent, etc.
The basic principle is such that item consumption would create GL movements (depending on inventory settings) - credit stock, debit adjustment account. Posting GLs would naturally affect GLs, and posting Resources - wouldn't.
If the job is finished within the fiscal year, companies choose not to bother with WIPs. These are calculated based on the WIP Calculation type and Job Posting Setup, posting recognized sales, costs, etc. Creating invoice for the job/'job task' would also generate PL entries. How you use them depends on the type of projects and what you want to see in your chart of accounts.
Sorry I can't give you more details on this, but this is a very big topic to cover :)