It was nice to see (seeing) you too. I always enjoy your company. Both 'to see' and 'seeing' are correct.
Twice in one week is not too much for me, but unfortunately I'm busy tomorrow (missing the future tense? I'll be busy tomorrow).
Can we meet up on Monday or Tuesday? If so, can we meet up somewhere closer to our homes? 'Meet on Monday' is the usual way to say it for an English person, 'up' is redundant. An American would probably say 'meet up'.
Student or Learner