is this the way i want to wire it?
Kinda.
First, match the fuse to the size of the wire, the length of the wire, and the current requirement of the accessory(ies). In this case you probably don't need (or want) a 30a fuse; especially if you are running 18ga wire to the battery. Read the info that came with the lamp, but I would guess a 10a fuse or less. I would recommend using the same type fuse that your Cruiser uses and that's an AGC style fuse. Most auto parts stores will sell an in-line fuse holder that is weather-resistant. That's the style that you want. You will want to add a ring connector to one side (sized to match your wire and your battery terminal) by crimping, soldering, and heat shrinking the terminal to one end of the fuse wire. You will solder and heat shrink the other end to your "red" wire going to the lamp.
Second, you can tap a ground just about anywhere. In fact, there is a factory ground point under the center console where you are putting the map light.
Lastly, you will want to put the red wire going to the battery in some split loom. Add it to a loom you already have or put in a new ~4' section. If you are planning more accessories (CB, 2M radio, inverter, etc.) then get a 1/2" dia split loom or larger. Otherwise use the smallest size that you can get. The split loom they sell at hardware stores (Lowes, Home Depot) is *not* recommended for use under the bonnet. BTDT. Go to NAPA or a speed shop and get the "gray stripe" type of split loom. The hardware stuff will last about 1 year with the temperatures you get in the engine compartment. There is a big rubber grommet on the firewall under the DS. It's about 3" in diameter. You can poke a tiny hole in this grommet to run your wire through. Then, use convoluted tubing (aka split loom) to go about 8" to the hole in the DS front fender, through the fender ~2' to another hole behind the charcoal canister. Exit there with the split loom and come up behind the battery box, through the rubber grommet in the battery box, to the +12v terminal on the battery.
You should be aware that wiring the Hella lamp this way will mean that you will need to be careful about leaving the lamp on. It will stay on even when you turn off the ignition, remove the keys, and leave the vehicle. Lamps also get hot when left on for extended periods, especially those with halogen bulbs. If it were me, I would select a switched +12v under the center console and
not run a wire directly to the battery.
Let us know if you have any more questions.
-B-