Washingtion DC

Can anyone recommend a hotel to stay in Washingtion DC, I am travelling with a group of 5. My father is traveling with us, who is 80 years old and isn't used to a lot of walking, so would like somewhere that would be convenient for him. Should I stay in a hotel near the metro?

Also, how many days do you need to see a decent amount of sites. Should we rent a car? Are there any bus tours you can recommend we do?

Any helpful tips would be appreciated. Thank you.