SEPM upgrade from 12.1.6 MP5 to 14

Hi,

I'm planning to upgrade my SEPM to the latest version which is 14. But in my environment i have bunch of client pc's running xp.I just figured it out for xp i need to install legacy client packages.

1. Is there any way that i can upgrade xp client machines only sorting out by OS ? 

2. Also what happens to the offline clients while upgrading as a group ?

3. After the upgrade do i need to upgrade LUA also or i can add the upgraded SEPM into my current LUA ?( current version is 2.3.4.16 )

If anyone can help point me ina right direction , I'd be truly grateful.