I would use connectors (male/female) on the connections inside the doors. Wire nuts aren't really for automotive wiring. Make sure they are the kind w/ covers so they don't touch anything and short out. You can cut the wire to length before you crimp the connectors on so you don't have a wad of extra wire laying inside your doors. You want a little slack, but not feet of extra wire. Use zip-ties to keep the wire out of the window track, etc. I would use a wire tap like these 3M ones to tap into the constant power and parking light wires:
That way you don't have to compromise the factory wire by cutting them. I'd do the same for the keyless if you have to tap into the power lock wires.
Use ring connector's like these (of the proper size for the wire and bolt you will be grounding to) for your ground connection:
Soldering the connections is the absolute best, but connectors, crimped properly, will provide a trouble-free connection as well.