Yes, it is hard, it is very labour intensive and you will pay for the labour. And please be prepared to repair your lath and plaster walls because accidents will happen with those long drill bits!
A minimum 100 amp panel is your best bet, I would recommend going with something higher with lots of breaker slots. The cost of a larger panel is only a few hundred dollars and it takes the same amount of labour to mount a 200 amp panel as it does a 100 amp. This may seem like a lot but consider the price of the entire job and future considerations. I know of houses that needed a new panel because they ran out of circuit breaker slots to feed garages or air conditioners.
Rewiring a house means bringing everything up to current electrical code. Wiring a new house costs $4000 and up. All that wire, outlets and switching add up. If your house is not knob and tube, you can do it in stages starting with a service change. After you have been in your house a while, you may want to renovate the bathroom or kitchen for example and the wiring in those walls can be done in stages.
You have a lot of expenses to deal with just purchasing the house. Live in it awhile and see how things go. Take the time to find contractors that you are comfortable with, and get references. If a contractor doesn't have the time to call you back or estimate the job, find someone else. And be prepared to stick to what you want. Don't believe that because you have an old house you have to "live with it". Piece of advice: everything you do in the house will take twice as long and cost twice as much as you thought it would! firstname.lastname@example.org