It can all be done ... but it will be money and time spent on a 10+ years old camper. It may be easier to go out and just buy a camper that is closer to your wants/needs. Maybe after you have used this one with minimal modifications for a season or two.
For the oven, you could just get a Coleman folding stovetop oven, or maybe an Omnia.
A fridge would be nice. I suppose retrofitting an absorption fridge into a camper that has none means a lot of installation effort. You need a gas line, electrical for 12 and 110V. Since the fridge burner needs a compartment connected to the outside air with vents and a chimney, this could be a lot of work.
A compressor fridge will be easier to install, but you will probably need to upgrade the electrical system (more battery capacity, solar) to make it work.
None of these are exactly cheap.
A water heater also needs a gas line at the point of installation, and you will need to rework the water plumbing.
If any of this is worth it to you, only you can answer for yourself.
Many campers came with all these options installed, including the upper bunk bed. It may be easier to trade your SixPack for one of these and spend the saved time and effort camping.