Is it definetly a 205mm you need? 229 is the shortest easily accessible one.
Try a 229, if it's a bit long cover the extra length, DO NOT CUT A BARREL DOWN, you won't crown it properly without a lathe and then you've negated the use of the upgrades completely.
Lubricating pistols is great fun for me. I hear allsorts being recommended by even my own co-workers:
Spray here, here, here, loads in here, give a bit in there and it should be ok.
What you SHOULD be doing:
Remove slide
Cloth/towell/paper to clean as much crap off slide rails as reasonably possible, should be grey coloured fine oil stuff coming off.
Spray on the piston head, quick spritz into the nozzle gas route
Small (2mm diameter) DROP (not spray) of oil onto the rails at the front and push it backwards with your finger.
Don't bother with the trigger mech, they're greased fine from the factory.
Any more than that or without cleaning the rails every time you re-lube and you're just making a grinding paste, accelerating wear on your pistol.
I don't suggest doing anything more than that on most pistols as they aren't real, and are going to break within 3-4 years MAX. maintenance is to extend the longevity of the product, but the product does not have THAT long a life anyway, so why bother.
Another tip, if someone asks to do something, ask why. If they know what they're talking about, they can tell you why to do something.