I am going to host 5 magento websites which include about 1000 products max each, about 25k visits per month each(max). I don't want to buy a server and waste its resources, either struggle so looking for suggestion on whats the best number of cores/RAM for a package like this?
For software specs you can check http://magento.com/resources/system-requirements
For the database please find a hosting provider that supports Percona MySQL
For hardware with a setup like this I'd say 2GB RAM and 2CPU should be enough but it depends a lot on how well the shop was built and the type of caching you are using.
Some tips on server configuration can also be found here: https://www.mgt-commerce.com/blog/magento-on-steroids-best-practice-for-highest-performance/