oracle 18 c xe database working report for 44 days work with no any problems
with web service and apex 5,1,4

hardware : 4 cpu 1.6 ghz burst 2.56 ghz( average 20-40%), 4 gbytes ram ( apps 60% + 50% swap linux) , linux centos 7 os connect to the internet directly with dinamic ip address, one plugable database install
xe pdb1

time to open web apex page : 2-3 sec