Update Exchange 2010 to SP3

Hi! I'm really newbie to Exchange. I've a Exchange 2010 server (all in one server, WS2008R2 SP1) into a domain with two domain controllers, the main is a WS2003R2 SP2 (AD, DNS and DHCP) is a and the other is a WS2008R2 SP1 (same AD, DNS).

If I create a user into WS2003 AD the user is created in both AD's. If I create a user into WS2008 AD the user is created in both AD's. It's the same domain.

My main concern is about AD scheme update.

1. Can I update from Exchange 2010 witout any service pack to Exchange 2010 SP3 directly?
2. Will the SP3 installer do all the AD schema update automatically or I need to do some manually (Setup.exe /prepareAD...)?

Of course, I will backup Exchange and Domain controllers before (they are Hyper-V virtual machines, so it's easy)

Thanks and sorry for my ignorance