Welcome to the dark side.
If you have never done model ship photoetch application, let me suggest that you stick with the PE which comes in the set plus the Dragon Buchanan upgrade. The photoetch set by Gold Medal Models is very nice, but it has much of the same items as are in the Dragon sets. It may be a bit finer and it will be easier to screw up. As a first ship model, believe me you will screw up. I still do.
I prefer to airbrush my PE while still on the fret while I am airbrushing the model. Apply the PE afterwards. It is easier to mask & paint first (IMO) than the otherway around. I generally do not need to prime my PE. It comes clean from the manufacturer. They have to clean it or it would continue to etch and you would have a baggie of not too much. You may want to give the PE a swish in lacquer thinner if you have been fondling it in your pizza-grease stained hands. I have likewise found that a soak in vinegar to give the part some 'tooth' is not necessary.
Rule 1: Measure twice, cut once. Use a pair of draftsmans dividers to measure between logical end points; previous rail runs, gun tubs, bulkheads, etc. Work in 2 to 3 inch lengths. Resist the urge to do the entire side in one piece just because you have a piece that long.
Use a #10 xacto blade on a piece of tile to cut the part fromt he fret. One finger on the part while cutting will help it from flying into oblivion. Use a sanding stick to smooth any nubbins. Plan on going back at the end on touching up any nicks in the paint.
Make your bends off the model. A Hold-n-Fold or Etchmate is not necessary. Bend between a pair of opposed razor blades, or a square-jawed pliers. Once you work through the sequence of bends necessary using a simple tool, it will make you more efficient with a more complex tool. [Remember just having the tool in your toolbox doesn't make you a better modeler, you still need to know how to use it and to practice.]
Round bends can be made around drill bit shanks. Bend one size smaller since they will spring back.
I recommend a white glue, such as Aleenes Tacky Glue, from the craft store, to tack the part in place. It grabs quickly yet allows time to reposition. Best of all is that mistakes clean up with water. Put a pin-point sized dot of glue on each end and every 1/2 inch or so. Place, postion, and allow to dry. When dry go back with a fine bead of CA applied along the gutter rail to secure everything in place.
Work inside to out and top to bottom. This will minimize your disturbing previously installed work.
Once everything is in place go back and hand touch up any nicks or cracks in the paint. A final coat of clear flat will blend everything together and will kill the shine of the CA.
The Buchanan is a beautiful kit. Because it is like many Dragon armor kits, "why do something in 5 parts when 20 will do", I tend to not recommend the kit to a raw ship NOOB, or one who doesn't have a Dragon tank or two under his belt. My raw NOOB recommendations with PE are the Fletcher by Tamiya, the England by Trumpeter, or the Emden/Dresden by Revell.