We often say verb+to+verb, but here is just to let you know?

[Liqichao]

hello guys,

here is the sentence:'Also just to let you know, anything booked less that 20 business days out will have reduced services.For this training, the main change would be you will be responsible for sending your own communications'.

I have some confusions;
1. we often say verb+to+verb, but here is just to let you know. why here does not say 'also just let you know'?

2. could you help me to tell book room or reserve? are they just sound different?

3. what is the meaning of reduced services? dose it means he will not offer the services which were done by him and distribute the work to me?

big thanks
best wishes
:D