Hello Op.
I've been with DP for 4 years but we don't live together. He has his own house and spends 50% of his time there with his DCs and the other half here with me and mine. Due to the DCs being settled at their respective schools and local friends, we have no plans to move in together any time soon.
It does feel a little bit like we're not properly committed or that people will presume that we are not serious. However, we have every intention of living together when the DCs are all grown up and less dependant.
Regarding your questions:
1) How long into your relationship were you introduced to their kids/them yours/kids to each others kids? How did you go about it? What problems occurred?
DP met mine within a couple of weeks as my babysitter let me down and his alternative suggestion was to take my DCs out to the cinema and for something to eat. I met his shortly afterwards. I didn't see the point in waiting too long, becoming attached to him and then finding out the DCs didn't like him or vice versa. Imo it's important that everyone likes each other and without that there was no future in the relationship anyway.
My DCs love him to bits. He's funny and kind and doesn't really parent them unless they're being really annoying so he is a very positive influence for them. His DCs don't spend that much time with us any more. We did used to spend most weekends together but it was quite stressful for me having a houseful every weekend, so we have scaled that back a bit.
We do have the odd parenting disagreement (having his DCs half the time he can be a bit more indulgent of them whereas I am a bit stricter and find it difficult when his youngest is treated differently, but I have learned to just step back and concentrate on making sure my DCs are happy)
2) When did you move in together? How did it work? Did you have to move into a new place together or did one of you move into the others house? What problems arose from this?
We didn't! Will probably either move him into my house or buy somewhere new once the DCs have left school and are a bit more flexible. Youngest is 8!
3) How did you find the time to spend alone time together before moving in together? How important is it to spend quality time with each others kids before living together
We get a night off together if my one day a week when the DCs visit their coincides with his kid free 50%! It works out OK most weeks and if not, my eldest is old enough to babysit for a couple of hours if we want to go out for dinner. We also meet up for lunch sometimes during the week, so we aren't lacking in time together despite not living together full time,