Correct me if you please.

Dear Joe,

I was happy to get your letter and to know that you (have) accepted my invitation. Kyiv is a very beautiful city and you will see it soon. I think that the best time to come here is during the spring/in the spring because it isn’t as hot  as the summer. The city is green and there are a lot/lots of flowers everywhere.

When you will come, we can visit a theatre or museum and of course walk around the city. Do you know that the main street in Kyiv – Khreshchatyk is the smallest main steep in Europe? We can go for a walk and take photos here and near other popular places in the city like The Golden Gate or Saint Sophia’s Cathedral.
I will be waiting for you to visit this spring. Write me back so that we can agree on the details.
All the best, Vi

Very good, Vi! 

Dear Joe,
I'm getting happy that you've accepted my invitation. Kyiv is a marvellous city and you'll see that one very soon. I think, The bestest time of this city is spring because it doesn't as hot as in summer, all the cities are surrounded by greenery and there're lots of flowers everywhere. When you'll come here , We'll visit some theatre or museum and of course walk around the city. Do you know about the main street in Kyiv ? Khreshchatyk is the smallest main steep in Europe. We can go for a walk and do fabulous photography at same place. There's other popular places in the city like The Golden Gate or Saint Sophia’s Cathedral.
I'll be waiting for you to visit this spring season. Please write me back to agree on details.
Best regards, Vi.