Two bridges (x86_64, statically linked, one bridge on each of 2 IP addresses) run comfortably in 256MB on CentOS/x86_64. This is with traffic up to 1024GB/month.
That said, it is best to have some swap space available for atypical operation (e.g. installing OS updates, etc.) On VPSs with only 256MB and no swap I have to kill one of the bridges for yum/rpm to work their update magic.
You will need more memory if running Obfsproxy, especially if it is linked statically. I can't be more specific because I am just getting started with Obfsproxy.
Regarding the build: It is definitely worth compiling/linking yourself, but not for glibc. You can't link glibc statically because libpthreads just will not link statically. The benefit of linking against zlib/openssl/libevent is that you can use the current versions of those libraries, rather than whatever your distro provides. (Even the latest CentOS6 version, released 2 weeks ago, has obsolete versions of all 3 packages.) And you especially want the latest openssl for its speed and AES improvements. Plus, compiling yourself lets you fully utilize the instruction set of your CPU.
One more thing. You wrote "vserver". If this is just shorthand for VPS, then you can ignore what follows. If you meant VServer virtualization, I would urge you to use another, any other, virtualization method. (E.g. Xen, KVM, VMWare, etc.) Mostly because ip{6}tables and certain system config variables will not be available to you in this not-really-virtualized-at-all environment.