Here's a question to help determine the technical requirements:
Is the content you want in the feed displayed on each product page?
If it is (even if you might need to cut description text down etc.) then you can write a fairly simple spec for your devs to simply pull out that data in the format required.
If you're non-technical but have good developers, then the easiest request is for them to pull product data out of the database in accordance with the published spec:
That spec itself is sufficient for a good developer to give you a quote for cost/time to complete.
Cron is the equvalent of a taks scheduler on windows. Basically you set a process (to create an updated feed) that runs on a particular schedule (e.g. weekly). That way you automatically submit a feed URL to Google that is always up to date.