Certainly do-able mate.
You'll need a Bluetooth HU so you can make and receive calls an output for your iPod, either on the front for convenience, or the rear (but you'll then need to route the cable).
You may need the 2 double din brackets that hold the HU in place if these have been removed. You won't need a huge budget, but on the other hand, you could spend LOTS.
My (non touchscreen) Alpine HU was £140, has Bluetooth and a USB port on the front so can play music from a storage device such as a memory stick or iPod. As it's BT, you can also stream music from your phone.
You may also need an additional loom for the steering wheel controls (if you have them) and a facia surround. Plenty of guides on fitting a HU on here and on the interweb.