For example if I say:
"The hardest thing is to get out of an air conditioned room and to walk into a hot kitchen."
would that be OK? I mean to use "to+verb" repetition in a sentence?
The easiest way to answer this question is to refer some authentic dictionary, and to look upon such usage in examples!
Yes, it's okay! :)
Repetition often reduces the quality of the script due to unnecessary words; however, many still repeat their sentences and don't receive serious criticism. Even sometimes you should repeat words or clauses in order to clarify your statement to your audience. But that's not the point here. The point is, it's perfectly logical to leave the "to" there and it won't affect the quality of the composition in any ways.
Additionally, as Maulik mentions in his sentence, it's really easy to find examples of sentences with more than one infinitive and then I would challenge you to a question:
What would you have replaced the "to" with if you had to make infinitives?
It's disgusting to let there be a downvote and not to bother to leave a constructively criticizing comment afterwards.
The most explainable approach to answer this question is to do it with adequate examples.
The hardest thing for a man to bear is to make him watch his family suffer.