what's proper way to tap into power?

On the older Land Cruisers, you can use the BLACK/ green or BLACK / YELLOW from the ignition switch itself. Test with a meter to be sure.

The rest of your info is correct.

Don't use scotch-locks or t-taps. Use a "telegraph" connection. Here's how: Carefully remove the insulation, spread the wire then feed your connecting wire through the center as if you'd be threading a needle, wrap it around once or twice and tape. This works good for low current applications.

I solder everything.  I'm not a big fan of the "threading the needle" method, but some people swear by it.

What it ultimately comes down to is how do you feel you would make the best connection?  If you've never soldered anything soldering probably wouldn't be the best way.  If you don't have a good set of crimpers (a dedicated set that does nothing but crimp and maybe cut wires) you probably shouldn't use crimps.

If you've ever used scotchlocks or t-taps you should already know not to use them!   haha

In the end, whatever method you can do the best will be the best way.