What is the process to maintain top ratings? Keep link buildinig? Keep producing fresh content? How is the ranking maintained?
You have it down: stay relevant. Do all of the things you've suggested above. Of course, that's a lot easier said than done, but if you've gotten into the Top 5, then you're not afraid of hard work.
Key thing? Stay ahead of your competitors who are right on your tail. Keep building links, new content is always helpful, and as others have said, keep doing what you've been doing.
fresh content backlinks link bait(make people talk about your site) paid links(this is the best option, as you can choose what is the best link for your site) write articles about your site.
Maintenance of Ranking is as hard as getting on Top of it. I suggest you do the following (This method is tested and proven): 1. Keep doing Link Exchange 2. Keep on submitting Press Releases 3. Always check the Keyword Density and Prominence 4. Look for some new Keywords and Terms for new prospects 5. Never ever be satisfied on your Rankings!
Stay relevant, keep your site updated, and keep adding fresh content. Also, keep building backlinks, even though your organic links will grow as well.
You got to the top 5, so, you know the work is hard and not easy. But I think you are on the right track with your ideas!
You should target for PR # 8 reaching at PR# 5 and look for retaining the backlinks and start branding your site.
Live in fear, keep doing what everyone above suggests, but know everyone below you had a big target on you.