To replace the rear main seal either the engine or gearbox has to be removed it is a 4+ hour job (for a mechanic who knows what he is doing) or 2 days if you have no idea. If it's a manual then it would be recommended to replace the clutch while engine or gearbox is out. However you would need significant tools such as an engine crane or gearbox lifter.
The water pump is slightly easier but will still take several hours to replace as significant parts on the front of the engine need to be removed. Again there are other parts that are recommended to replace while the front of engine is apart such as timing chains.