Converting/upgrading a ship

Unfortunately, the dragon class isn't even remotely canon (I found that out to my own disappointment a while back, as I had been planning on using the design with one of my characters). The actual source of the design is Wizards of the Coast (in one of their D&D magazines, as a fan supplement design for the D6 SW system if I'm not mistaken).

That's our test? ... >.> tries to hide the crate full of manuals, catalogs and guides to acceptable cannon sources.

My $0.02:

Based on the last picture, if you're going with something in the 400-700m range, I suggest that your ship pack a heavy forward punch, with surprising maneuverability for a ship it's size. However, this might come at the cost of speed(which is really acceleration in space) and durability(all those external hard-points make nice targets for bombers). (though as a pirate, you'll not likely run into many of those; unless you get caught) you might also have difficulty maneuvering through atmospheres, so much so that your character would normally break off pursuit with this vessel in orbit.(other vessels could still give chase easily)

The spars look like they could be used for weapons emplacements, fighter racks, and docking/boarding points. Also, given the skull/artistic bow, you might have a small blind spot in weapon arcs directly forward(maybe out to 150m if it's a 700m vessel). Inversely, those same spars would provide shadows, where hull mounted guns couldn't reach. (sorry, no shooting through yourself). So think about what you want your ship to be capable of, then think about how it would achieve those goals, and what risks/weaknesses it might have while doing so.

For instance, you might be able to slug it out with an MC-30 if you're facing it head on, but probably don't have much of a broadside to offer, and most of the aft being thrusters for greater maneuverability, and possibly short bursts of acceleration(best used for ramming), will have almost no return fire to offer an MC-30. (which isn't to say you have no fighter defenses, just nothing to hurt an MC-30) Does that make sense or has my excessive analysis of lost you in mires of words, numbers and hypotheticals?

Roles:
1) May I suggest Pulse-mass Mines? (of the Hapes Consortium, originally)
2) Looks like you want Heavy/LR Ion Cannons for your main gains, possibly a mix of the two.
3) Lining the aft surfaces of the pylons with small(er) sublight engines will provide ample agility for a ship it's size, without costing much from max speed/Acceleration. As for high/low speeds, a craft will always be more maneuverable at low speeds in space, due to inertia. yay Physics.
4) A thick hull, even just on the main hull(not counting pylons) would allow you to take a beating, and the pylons being extended from the hull, would be relatively easy to repair/replace as needed. Standard shields for size will be fine.
5) I suggest ~600m then. It will leave it able to fend off most corvettes and many light escorts in the Imperial and Republic's navy's.
6) Tractor beams are the most common, though some designs do still use actual tow cables. (Most notably the infamous snow speeders) There are also other technologies that perform similar functions, though some of these are rather restricted by race. There are ways around this, so if you find one you like just say so and I'll help you work out how you got a hold of that bit of tech.

Weaknesses:
I'm curious that you've not said anything about carrying fighters for this vessel. (that's fine, more room for other piratey things) Will you be expecting this ship to rely on escort carriers? (ships made/modified to carry large quantities of fighters often with little room left for ship-ship defenses) The weaknesses listed are good(with the exception of 4 which is true of all ships)

In regards to the canon ship reference, I believe the RPAs have agreed to permit the Dragon-class as a reference. I certainly don't mind the reference. (I suggest you introduce/describe your ship as a custom piece designed to be similar to the unique vessel). If that gets overruled/changed we'll be sure to let you know.