Mntb

I'm new to the site. Hopefully you guys can help me out.
A friend of ours bought our 2005 Chevrolet Equinox awd 3.4l. We owned it for about 6 month.

Can someone tell me what spark plugs to use as replacements?

Can I use platinum or double platinum?

She doesnt have a lot of extra money, hence the reason why I will be doing it. It is hard to find any info on the '05-'09 Equinox or Torrent (pretty much the same thing).
Does anyone know how hard it is to replace the lower intake gasket on this vehicle or a rough idea of how much a shop might charge? It has a small coolant leak between the head and lower intake.
Can she use stop leak until she can get it fixed?
I have some mechanical ability and I like to learn new things. However, I have sticky hand tools, no air tools. I do change my own oil, spark plugs, wheel bearings, brake, etc.
Id like to have an idea so she doesn't get taken advantage of. This is her only vehicle right now.
It's difficult to find any online info on this vehicle.
Thank you in advance.