Fictional characters re-imagined as RT characters/classes. What would Han Solo or Kirk, or Mal be like in the RT universe? What would they have as a ship? Crew?

One of the fun things about 40K is that the size of the Millennium Falcon or Serenity is such that your average Imperial vessel could ram it and probably not even notice. The Enterprise would be noticed by anything of Light Cruiser size or smaller. Probably.

So for smugglers this actually works really well. They're in possession of some small, archeotech vessel with a reliable superluminal engine comparable to a Navigator's warp jump, and a complete and certain knowledge that the Mechanicus would tear them apart to get it so they embark on a life of light piracy while still staying true to their morale code because they're outside of the Imperium. Small-r rogue traders for sure, making a profit moving a few goods or people around and disguising their ships as hunks of junk that would be mistaken for in-system traders whenever they're caught.

What's more fun is Chewbacca. He's obviously a Kroot that ate a Wampa, absorbed its genetic predisposition to extreme hairiness and only communicates in his own language rather than Common.

Kirk would be burned by the Inquisition for whatever they would call bestiality when you apply it to Xenos. Possibly bestiality.

Well, "incest", as a word, doesn't seem to imply whom you are with, as much as simply impure that you were, so perhaps Kirk would just be flayed alive for that, or, if I want to put a needless twist on the word, and partly do to Latin what GW has, in the past, I might say xenocest. Don't know, sort of don't care; they'd burn Kirk for it , but if it was the Adepta Sororitas that caught him (his luck), he'd still hit on them, the whole way to it, and they, being the Battle Sisters, would not be impressed. Still might be slightly better than the "official" way Kirk died, though there he was a hero, whether Picard updated history, or just let it stand.

Solo and the Firefly crew? Yeah, they'd be a bit more interesting, both having personality, and coming from a less shining government, in their universes. Sadly, an Imperial fighter craft is approaching the same size, or at least same crew size, as either the Millennium Falcon, or the Serenity, so I think they'd find competing with the imperium's vessels, under almost any circumstances, difficult, unless they specialized in hauling only the most compact, exotic, expensive goods, that only their personal character traits allowed them, and no one else, to get their hands on; in this game, if I am not being dumb, regarding the Serenity's size (Internet says 270'/82m long) a "transport" in 40K can modify its hold into a fighter bay, holding up to two squadrons of 55m assault boats, or slightly smaller fighters/bombers, meaning that the difference in what they can lug is massive.

I still think they'd be fun, as both would flout the gov't in this universe, and both have a certain amount of experience dodging the authorities, of their respective galaxies, but I still think they'd both find the 40k universe impossible to live in, as their respective verses have at least some small hope for things to get better; in 40k, there is no better. Either the Emperor dies, and the Imperium gets eaten, He wakes up, and lets be honest, He wasn't always the greatest "benevolent leader", plus His impression of the current Imperium would probably make for another civil war, or nothing happens, and the oppressive status quo is maintained. That leaves the galaxy to either get flensed by Necrons, eaten by Tyranids, washed over by Orks, or just +++-****ed by Chaos. Grimdark means "no happy ending", even WITH an Ambassador aboard your ship.

Fictional characters re-imagined as RT characters/classes. What would Han Solo or Kirk, or Mal be like in the RT universe? What would they have as a ship? Crew?

I think what you are asking for is what cross over characters would they be in 40k, along with a ship comparative to a similar class as theirs from their original universe? Is so, read below.

Han Solo would either be a Free Captain, or a RT with very little PR that won his ship in a card game (sounds like a NPC FFG created doesn't it?). Han would also have a few Xeno's on his ship, possibly in leadership or other important position. As for what his ship would be, probably a Small Frigate or a Raider like a Cobra.

Mal would be a Free Captain, or maybe a very low PR RT, but I would say he was a free captain skirting the law. Ship would be a fast Transport, like the Orion / Viper / Scout whatever it's called. His crew on the other hand would be more interesting than his ship. A second in command AM, a Missionary (probably of Drusian faith), ex-bounty hunter AM, Void Master, etc. etc., would be accompanying him everywhere he goes, and bailing him out of whatever trouble he somehow manages to get himself into that day of the week.

Kirk, well, he would be a Captain in the Imperial Navy, with probably a Light Cruiser called the "Enterprise." He would probably be more open minded than most other Imperial Navy Captains, like a certain female Navy Captain in a FFG adventure. His exploits, adventures, and fame would be known to allot of people in the Expanse. Xeno and RT alike.

Note: Don't have my books with me, so ship names and it's class might be slightly off the mark.

Also thinking on what their stats and class would be. Kirk is most likely a rouge trader class, with an eldar first officer. Kirk ws 40, bs 35, str 35, t 37, ag 37, int 40, per 41, wil 38, fel 55.