Maybe it doesn't matter anymore, but here's how I got a Kestrel, the route I took to get it, and the reason why I got rid of it as soon as possible.
Of course, I start with the little shuttlecraft, and then get a scoutship A.S.A.P. so that I can do more than one mission at once.
Next step is getting the 750k for an Argosy, which is (in my opinion) a great ship. Load it up with armour, all the shield capacitators it'll take and then fill up the rest of the space with missiles and racks. You should be able to take down Corvettes with ease, and Kestrels/Frigates/Destroyers can all be taken down with Argosies. Oh, and get rid of those feeble laser turrets, and get proton turrets instead. Add in all the manoevering upgrades, and you have a battle ship (I got tritanium for mine - you'll need a couple of mass expansions to take in everything). Then I do the Diphidia II mission - that gets you 1mill. credits, and with your ship trade in you'll be able to afford a Corvette when you finish the mission string on New Istanbul.
A word o fadvice - if you see a derelict like the S.S. Forrester, board it to get the pirates to jump in, then just disable them with missiles. Board 'em and get the ships as escorts - now you have some real firepower. Alternatively, you might want to nick their ship for your own. A rapier is a nice ship. But I prefer a bit more shielding and armour.
With a corvette, you have to get rid of the javelin pod/javelins and heavy rocket launcher/heavy rockets. This frees up a lot of space. Now ditch the laser turrets and replace them with proton turrets (if the feds hate you, then Akio sells them, incase you thought Sol was the only system to sell them, as I did for a while) Buy all 3 types of armour (yes, I know it takes up 65 tons, but it's worth it in battle) and 4 shield capacitators. Now your ship IS kestrel-class in terms of shield. Buy a missile jammer, and all the 3 manoevering upgrades, and suddenly your ship is lightning fast, and as manoeverable as a fighter, whilst being super strong. Basically, avoiding any weapon as easy as pie now. Okay, so it cost a bit, but then all you need to do is hang about in Darven or ALtair, or one of the pirate systems for some good ships to come around -you CAN take on anything, ANYTHING with this beast of a ship. Well - almost. But Kestrels are easily disabled, just pound em with missiles and then shoot em with the proton turrets to finish it off. 400k, easy peasy. If you don't like battling, then just get a good combat rating, and land on a pirate planet, in the bar you should get the UGE mission string - 100k missions in the mission computer, very nice. I find that if you transport a 'fed criminal (shady guys who say your ship is fast, and offer you 75k to move them to a pirate system) then you get the mission when you drop the criminal off.
So, anyway, you've got your super corvette, and you're considering the Kestrel upgrade. Let me put it this way - the corvette is easily good enough to complete any rebel or fed mission, and, in all honesty, you'll want a cruiser of some sort when finishing the artemis group missions. So the Kestrel really isn't needed. Sure, it's nice to have the lightnings in their bay, but I had 6 rapiers as escorts with my corvette, and at 1million a time to replace, it was too steep. And besides, I don't think the Kestrel is manoeverable enough to do justice to it's 10mil price tag.
As a final note, here's a funny glitch in the game that can net you just over a million credits. I did this in my rebel cruiser, whether it works on ships without docking bays I don't know, but anyway... WHen you disable a Kestrel, try and leave the two lightnings so that they're buzzing after you - just avoid them, it's easily possible. Board the Kestrel, and if you capture it, the lightnings will stop attacking. Tell them to return to the mothership - and they'll return to your ship, so you just sell them off at a considerable price each time. Easy money. And the Kestrel you nicked 'em from will still have 2 of it's own lightnings. So you don't lose out either way.
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