Browser settings do not use memory.
Memory requirements for some privacy extensions can be found here.
Hostlists do not require extra memory. The Hosts file is a feature built-in within the Windows OS. If using a hostlist, please be sure to first *disable* Windows DNS cache client service. If not, you will experience the "svchost takes 100% CPU time" issue. For easy hostlists management, I suggest using HostsMan, with additional lists.
Blocking browser's / other program's stuff can also be done via external, standalone programs, at user level. Please see :
- AdFender (more or less great)
- Ad Muncher (*much* better, uses regexp, very little memory used, but might not be compatible with modern OSes, and is probably useless for https filtering).
Browsers can be vaccinated with SpywareBlaster. Additional anti-Adware external list for IE SB customblocking.txt can be used as a complement.
Browser vaccination also exists in Spybot 1.6.2, but its vaccinations are outdated imho.
Browser vaccination uses no memory.
Regarding Hola, the FAQ says it is also available as an application (.exe) for Windows.
If using any kind of P2P software, you should check PeerBlock. You can use additional, free blocking lists from iblocklists.com, to improve security (use at least BadPeers, Hijacked and WebExploit additional lists).
Hope it helps.