Yes, this can be possible. You can import images as per the listed steps in Importing Boot Disk Images. In the same article, it is stated that the image must be “disk.raw”
You should able to convert vmdk to .raw format using tools like qemu-img and compress the file to .tar.gz and later creating custom image by following instructions.
As per the hardware capacity, it is not a problem. You can customize a machine type or choose from one of the predefined ones. Details can be found here.