5k can get you a lot of good stuff already... High end HU about 1.5k, comp speakers 2.5k, power amp 1.5k... These are just estimates.. but definitely will get you high end stuff... Unless you want a subwoofer which needs caps and extra power amp, then your budget is more than enuff..

Hahah.. I'm not expert in ICE but can help you a bit... For shops, you need to scout around or find thru word of mouth cos not all shops (sometimes even the established ones too) are good..and also look out for imitation products as they are everywhere...

The best way to configure your system is to browse thru the internet sites (sony.com, kenwood,...) and see the products they have... you can also google some reviews for the products that you have chosen.. After you have a complete list of the exact things you need, then go look for bargains..but remember, if it's too cheap to be true then it probably is...

I would recommend you stick to branded and established brands (Sony, Kenwood, Alpine,...) as they have accurate model numbers and code so you can trace their authenticity.. They have cheap mid range models too which have good quality... For the component speakers, yes they come with a crossover module and tweeter...

FYI, The difference between those non branded stuff and branded ones are of course the reliability and next is the sound quality.. non branded stuff (especially speakers) tend to be hard to tune as the tonal response might not be flat...