Best Config / Instance for Magento 1.3 on AWS EC2 RDS

Hello We have a dedicated server currently and wanting to move Magento to Amazon Web services.

We have 1) Magento 1.3CE ( will be upgraded in the next few months to multi store ). It uses APC cache currently and CDN. 2) 1500-2500 sessions per day : Typically 10-20 concurrent users and fortnightly 20-70 concurrent users for a few hours - very occassionally 200 concurrent users. 3) 10 wordpress sites - latest versions ( one integrated with Magento ) 4) All running MYSQL , PHP 5.4

We want 1) Room to Grow 2) Use RDS 3) Enough grunt to be very responsive 4) SSD

I have narrowed instances down to m3 , c3 or r3 AWS instances.

Question : Which instance is recommended - and ( assuming UBUNTU ) what default should I load ; some sort of LAMP Stack ( should it be without MYSQL because I am using RDS? ) . any thoughts appreciated.

Thanks so much for your time :-)