need help in letter of invitation HELP ME PLEASE! I'M RUNNING OUT OF TIME!

hallo there,
I woul be very greatful for some help in correcting a letter I have to write to another school to invite them into our school. Back in the days we spent some days in their country, and now it's time to re-invite them. The letter should be a fomal, polite one. My only problem is that I am very bad at letter writing.
thx for your help in advance
here is my version:

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Dear Headmaster,

Although we have been very busy with the home affairs in our school – M. G. retired, we elected a new headmistress Cs. S., and we have two new deputy headmistresses-, finally, we have time to deal with our friends.

We would be more than happy if you could accept our invitation for next year 2006 to . We can receive 30 people. You could invite your colleagues, relatives, and friends as well.

The programmes would be a matter of discussion between you and us; accordingly we are expecting your suggestions. Please let us know the exact time you can come, so that we can make plans for your accommodation.

We are looking forward to seeing you.

Yours Sincerely

XY