Painting your interior plastic pieces CAN be done. However, depending on which pieces you want painted, it can be difficult. For example, if you want to paint the trim around the radio, that can be done fairly easily. However, the dashboard since it is texturized, will require some prep work.
As far as the gauges, that really depends. You have to look at the gauges to determine if you have LEDs or wedge bulbs. If you have wedge bulbs, you can just swap them out (assuming there is no color filter/film on the gauge). If you have LEDs then I would recommend contacting a specialist and swap out your LEDs. Do NOT attempt this if you have no experience soldering, as you may ruin the circuit board.
Lights under the Dash (floor area) can be done fairly easily. Just make sure to use relays before you fry any wires. The Dome light is very very easy...remove trim, remove old light, install new light, re-install trim, sit back and admire your work.
The headlights will be difficult if you have little to no experience and/or patience in dealing with headlights.
If you have doubts, I would recommend taking it to a body shop or an import shop and ask them to do it, so if they screw up, they are financially obligated to get you a new one.