How can I encrypt my system (at best using lvm + dm-crypt/luks) such that suspend to RAM works and that everything is in an encrypted state when suspended to RAM?
What you're asking for is not a simple suspend-to-RAM, which leaves the RAM powered on and shuts down everything else. Since you'd be wiping cleartext process data from RAM, you need to marshall it all to the suspension image. So you have to invoke the hibernation (i.e. suspend-to-disk) code. The realistic way to do that would be to create an encrypted ramdisk, declare it as swap space, and fill the memory with other processes. Even then kernel data would not be encrypted; to do that, I think you'd need a sizable kernel patch.
On the other hand, if you're willing to suspend to disk, this is a solved problem. The hibernation image is stored in the swap space. Your swap space should already be encrypted given your security requirement. Make sure that it is encrypted with a known key and not with a random one (some setups with encrypted swap use
It stores your encryption keys in your computer's trusted platform module.
Another option may be TRESOR, which uses CPU registers to store secret keys.