If you have to run BGP, the big question is why and how.
i have one isp now,
because i want to add remote ddos protection from other service provider to my servers,
and i should setup my own AS and BGP to make it,
by the way,i need a router to handle it.
BGP is usually needed if you have multiple upstreams. And then the question is how will you separate the traffic between these upstreams.
In this case you might need to load full routing tables to get the optimal path between your multiple upstreams. And this requires lots of memory (several Gigabytes).
A CCR-1036 or CCR-1072 can handle this. (recommended: get the models with -EM which have even more memory). A CCR-1009, while being able to handle the CPU load, can not handle this as it doesn't have enough memory. In this case you can help yourself with filtering rules to reduce the routing table to reduce the number of entries. Meaning you send traffic outbound over one ISP and only short paths over another.
i think i will not have over 5 upstreams basically and shortly,
for this situation,
should i still need alot ram ?