You can check your electricity bill, it will state there. Even the solar companies will ask for a copy of your bill. If you are not staying there, just use your current bill and guesstimate.

Not so easy to add all your appliances, because of a few factors:

1) hours of usage may vary day to day, season to season
2) you might also change your appliances over the years
3) you might add new appliances too

As for following your bill, it is far from perfect too, as it also depends on your usage that month, but you could get, say maybe 6 backdated bills and average out the usage. To estimate the solar power, you cannot buy the exact amount as shown on your bill, as the solar panels do not charge at 100%, I would say you need to add another 25% on top of the monthly bill. And solar panels will depreciate its power over the years, so your 5kw system could be only 3kw after 10 years.

Are you planning on an off-grid system? If yes, you still need to find a big enough battery to store all this power.