There are tons of HU choices, as well as speaker choices. Pioneer, JVC, Blaupunkt and Kenwood are some good brands for HU. For speakers, look at Pioneer or JBL coaxials.
A basic HU will cost ~3k, which leaves a 7k budget for 4 speakers and wiring. And believe me it is tight, so it will be better to get only good front speakers now. Wiring can be laid for rear speakers as well as one go, so that you just have to get the speakers installed the next time. Wiring will cost you 1k, or 1.5k including labour charges and other small bits. Get good component speakers for front from JBL, Pioneer, Blaupunkt, etc. for around ~4k and if budget allows, get 6x9 inch coaxials on a tray for ~3.5k more.
What is your music preference? More bass or more quality?