Should I run several applications in Docker in a single server?
Yes, sure. As long as your resources are enough (i.e., you're not running out of RAM, HDD, CPU, networking), and as long as you are fine with one gigantic single point of failure, there is no reason whatsoever to not run many docker containers on one machine.

Keep in mind that the overhead of docker is really small - it's all just namespacing on the host kernel, it's not like you're spawning copious amounts of VMs or anything like that.