here is the spec sheet for this washlet. The second page shows the full dimensions you need to make sure this will work for you.
This washlet does need a GFI receptacle close to the toilet. The washlet comes with a 3 foot cord. It would depend on how handy you are as to if you needed a professional to install it. It is not much more difficult than installing a toilet seat.
Can you sit on the lid?
Toto does not reccomend sitting on the lid to the washlet.
It is mounted on the wall but it is wireless, so if you wanted you could just hang onto it instead of moutning the it.