No you don't need to submit a reconsideration request if you haven't received anything. Chances are you got hit by a combination of Penguin and Panda. They may have just refreshed one of the updates on the 8th. Looks like no one really knows exactly what it is. Because you're changing your link structure around, check your Webmaster Tools 404 errors to make sure something is buggy.

If you added /rental-type/ to setup the keywords and the pages both pages for regular rentals, condo rentals, townhouse rentals, for Baltimore are unique then don't bother changing your structure around. You're better off optimizing the pages further if they need it, then checking the pages linking to you to see if something has happened to them. If you have links from someone caught selling links, you wouldn't have seen a penalty but their links wouldn't pass as much SEO juice.

Yes the URLs like this

domain.com/rental/123456-123-Street-City-State-Zip

are better than

domain.com/rental/123456

I'd make that change right away if you're just using an ID to reference properties.

It's really best not to change your URL structure around. If you really need to, then definitely make sure you have 301 directs all pointed from the old links to the new ones.

The permalink keywords in the middle don't really apply as much weight as they used to. Using /home-rentals/ and /rentals/ won't immediately relate the pages to those keywords anymore. So with that, set your structure based on the different sections of your site so they don't conflict rather than inserting keywords. So example: "domain.com/search/california/" doesn't conflict with "domain.com/category/california/"

I need to see your pages to give you a better response on the last question. With permalinks, it's always good to match your page title with the page's main keyword. So if the title is 123 Street Ave then the link should be /slug/123-street-ave/. The slug is whatever descriptive keyword for that type of post is. It would be /search/, /category/, or no slug at all.

That doesn't answer your question for the SEO decline though. Chances are you've been affected by the recent Penguin 2.0 update. I'd start by checking my links and seeing if any of those sites got hit. Also check your webmaster tools and see if any notices have popped up.