The size of your repository defines how much disk space you’ll need; it’s a very simple calculation. Content is stored directly on the disk by default. Therefore, to hold 1000 documents of 1 MB will require 1000 MB of disk space. You should also make sure there is sufficient space overhead for temporary files and versions. Each version of a file (whether in DM or WCM) is stored on disk as a separate copy of that file, so make allowances for that in your disk size calculations (for DM, use versioning judiciously).
Use a server class machine with SCSI Raid disk array. The performance of reading/writing content is almost solely dependent on the speed of your network and the speed of your disk array. The overhead of the server itself for reading content is very low as content is streamed directly from the disks to the output stream. The overhead of writing content is also low but if Solr is installed on the same machine, additional overhead should be allowed for the indexing process.