Hi Ben, great name by the way. Welcome to the forum.
I have Jamex coilovers on my TDI (adjustable) and have them at about a 45mm drop (I think, I've changed it a lot!) - £300 from ebay. Very pleased with them & a friend (and fellow member) has them and is pleased too.
I just fitted them and that's it. No issues with the ARB or anything. I did do new top mounts at the same time.
Next time you're outside, just take a peak under the car and look at how low the sump is - be careful how slammed you have it. I am currently driving round with a cracked sump (a very minor one) and I got that at my current amount of lowering. I'm not a mental driver, it just happened!