I think it depends on the CMS that you use, it has two versions, free and one of payment, the one of payment is very cheap for a VPS, I believe that it can interest you.
@legend this can't be done via support forum you need to check this with the developer they should make varnish vcl file which need to support vhosts/sni system.
alternatively you can try php redis cache with magento which is way better than varnish.
@legend you can use both webserver nginx + apache and elastic search is completely depends on script side compatibility its nothing to do with webservers.