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Traditional pirates (c15-c18) had two goals: first to make money (to keep their crew happy); second to gain better ship(s) that they could then sell off as 'prizes' or use to increase their fleet strength.They would generally keep anything they could immediately use, ransom (or sell as slaves) the rest of the crew and/or passengers, sell off the excess cargo & keep or scuttle the hull. Pirates of that age should not be confused with Privateers: the latter were legitimate privately-owned ships carrying 'Letters of Marque' that justified & legitimised their actions on behalf of their country's government (along with associated legitimate prize rewards awarded by said government) towards Hostile Powers designated by their Government; the former were purely freebooters, not generally associated with any government, country or any other power (although pirates sometimes offered their services as privateers in exchange for pardons + loot - Edward Teach for example became the legitimate Governor of Jamaica for a while). By contrast modern (c20/21) 'pirates' usually ransom their prize (crew, passengers, ship, cargo) due to the logistics difficulty of keeping & utilising such a prize for themselves, plus modern communications & surveilance advantages
In X:R we can currently ignore crew morale & passengers, so it's up to <player> to prioritise cash, cargo or hulls as they see fit..
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Internal: If <target> is non-hostile you can dock. Enter the 'shed' (the small covered structure directly in front of you, often containing lockers) & at the back, to the right, there is a shield control panel available for you to hack using the craftable Security thingy. If you successfully hack this the ship's shields will be disabled for a time <5mins? Needs checking> (all the main shields plus most of the turret's shields on a warship). There's a similar panel elsewhere to disable turrets, I think.. but you probaby won't want to hack the Repair panel in the 'shed'! Shield hacking will significantly reduce the time required to board <target> if that's your objective, as you can immediately start reducing hull strength when you're ready rather than fighting your way through shields first..
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You'll want to intercept <target> & destroy their engines/Jump drive as quickly as possible while out of range of any hostile stations or patrol ships to avoid 'helpful' friendlies destroying your prize & boarding crew. The TO DLC adds a 'Constrictor missile' (only available from TO sectors' Arms Dealers) which disables boost for a time when (if) it hits.. Full operational details for this missile are not currently available. Another method is to mine the engines with the Traitor drone, then remote-explode the mines when the ship moves to a convenient spot*..
*I'm unsure of the range of remote-detonation. IZ certainly, but it may extend beyond that with the reworking of game range mechanics as described elsewhere <Sparky please provide link>..
A Rahanas freighter is an easy boarding target on paper only. Its hull is so weak that a slight miscalculation or stray shot may destroy the ship with your marines onboard, & it has so few defences that its main asset other than its cargo (its drones) are at great risk of being lost to Yisha's boarding demands (destroy Drone Bay). If possible choose a Sanahar over a Rahanas: the hull is stronger, defences are better & (slightly) more numerous & its speed & maneuverability is much improved over the earlier model. Once you have the technique, it's just as easy to board despite the slightly increased BR <Sparky please link to boarding pages>
If you want the cargo
You can hack <target> using the Trojan drone, or board them. If you hack them be aware that ejected cargo containers have a 'lifetime'; if your pickup drones don't get there in time the looted containers will self-destruct.. so make sure you have a suitable cargo ship nearby & available before you start this procedure!
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CHECK FIRST using your scanner & target information system to see if there's a market for the ware(s) <target> is carrying! If the wares are unsalable (currently eg (v4.00b2) Plasma Jets & Hailstorm) then a lot of profit is lost immediately. HOWEVER you can still sell the ship with its cargo to a convenient shipyard to recoup at least some of the cargo's value* REMEMBER that you can always transfer excess unsalable wares to a ship that's going to be sold, provided it has an intact drone bay..
*Probably its average value as defined in the Encyclopaedia, but there may be a discount; I haven't checked
Collector/Badass
Pick up tips from the above, then go ahead & do what you want; you won't listen to me anyway 
Boarding & Reputation (loss)
Rep loss currently appears to be calculated mostly by the number of hits you land that do hull damage (as of v3.61). There may be other factors, such as comms traffic etc.
Therefore you want to do the max hull damage (to take <target's> BR down to a number you can handle) in as few shots as possible. If <target> is initially neutral to you, or you're confident, Traitor drones' mines are ideal for this (after you've done the initial hacking as mentioned above): they'll instantly take out most critical systems (& a fair amount of hull on most freighters) in effectively 1 shot! Plus you can use them concurrently or consecutively to set off all planted mines at once
Once you've boarded <target>, as always transfer a 5* engineer to it ASAP. Not only will this improve its speed as its engines are repaired, but it'll repair the hull & turrets too (quicker if you're OOZ). A fully repaired hull sells for a fair bit more than an immediate capture, & you can recall the engineer (& captain if you've given it one) before selling the ship if necessary
*Probably its average value as defined in the Encyclopaedia, but there may be a discount; I haven't checked
Collector/Badass
Pick up tips from the above, then go ahead & do what you want; you won't listen to me anyway
I'll add to this later.. I'm going to bed now