Things to see

This year the Keukenhoff closes on May 21st.
Here is the official site where you can buy tickets https://keukenhof.nl/en/
Not clear if you are talking about staying in Delft or Haarlem as a base to explore Amsterdam on a day trip.
You picked Anne Frank Museum and the Keukenhof Gardens already. Take a canal cruise or walk the city should do for 2 to 3 days.

Hopefully someone from the Netherlands will help with lodging and restaurants.

If you mean Haarlem or Delft as a daytrip, I find Haarlem a more interesting city. It has a beautiful Market square, is wonderfully situated on the river Spaarne, and has two good museums (Frans Hals and Teylers). Delft is more touristy. But with the Keukenhof closed, you can easily do them both. And Delft can easily be combined with The Hague or Leiden, which you'll pass on your way to Delft.

Tickets for Anne Frank are hard to get. If you want to go there on May 21st, you need to log into the Anne Frank House website exactly two months in advance (March 21st) around 8 a.m. Amsterdam time, when they release the tickets (be aware that this isn't a firm time, it could be later in the morning). Many have reported that they go fast, so even if you have to stay up late in the States, it will be worth it. Otherwise, you have to wait in line for day-of tickets, which go on sale at 3:30 p.m. but visitors line up starting around 2 p.m. in the summer.

Can I buy tickets to Keukenhof Gardens on arrival or must I buy them earlier. Also, I am handicapped and use a scooter. Will they wave the entrance fee if I just show up?