Welcome to the Q&A Forum

I wouldn't just go ahead an do it without looking into it further, maybe waiting for more comments on here to weigh it up. It sounds counter-intuitive to me.

Hi Steffen, You shouldn't see a decrease in your SERP's for the page the images are on, assuming you keep the alt and title tags the same. Google may even see the new URL as a update to the page, which has its benefit. If the images are ranked in Google image search, you will obviously have a drop in that image ranking. You can fight this by 301 redirecting the old image to the new image as well as updating your sitemap. Here is a great link on the subject including a response from Rand explaining it more http://www.seomoz.org/qa/view/52713/301-redirect-an-image

Hello, It is definately a bad idea. It is simply because google can not detect that your page is not present due to your supply shortage, it yust sees that page is present sometimes and sometimes it is gone. Now ask yourslef: would you refer somebody to your friend who sometimes does the work that he is asked to do and sometimes he just quites in the middle. I think you should rather refer one who is always there and can be trusted. The same with webpages. No matter how good your page is is it unavailable for shorter and longer periods on a regular basis than it is not trustworthy. You should rather simply wite to the product that it is out of stock. Not to mention that it is much easier to solve this in your cms.

I would recommend using a 301 redirect to the home page as this will pass link juice. If they can be redirected to the specific product category that would be useful. An alternative would be to still serve up the old page so it results in a 200 code or a 301 to a product suggestion page. Having a products like this suggestion page and or a search for products page would likely convert better than just a blanket 301 redirect to the home page. Another thing you could do is create an intelligent "catch" page that uses the search parameter (if there is one) or the title of the page referring the site and use that as a parameter for searching your products database and serving up some relevant products.

Make sure you do the url to url wherever possible. If you don't, you won't know in a couple of weeks based on my experience. (One of the best pieces of SEO advice ever came about that very issue. When we went back in and changed each url to 301 within days we saw DA and PA go up!).  I look forward to hearing your progress. Robert