Darrell,
A 2000 watt inverter will run a residential refrigerator very well with power to spare, especially if you use one of the new very efficient Samsung units.
Your house battery bank will not be "overpowered" by a larger inverter unless you put higher demands on it than you do with the one that you now have. The difference is that with a larger inverter, you will have the ability to put higher demands on the batteries, so a little self control may be needed.
Personally, I would only consider a Magnum inverter as a replacement. They have the best reputation, are repairable if needed in the future, have excellent product support, and they a made in the USA.
With a residential refrigerator, your current 4 battery house bank will work if the batteries are in good condition, but they are marginal. If you dry camp dry camp very much, most owners increase their battery bank to 6 batteries.
The average do-it-yourself mechanic should be able to install a new inverter. However, since I do not personally know your ability level, there is no way for me to answer your last question.
Gerald
