overstay and duration

Hello,
I have a few questions. Firstly, a few months ago I had a double entry visa and I overstayed the second entry for a few days. This was sorted out without problems by the exit entry office and I got a new one (for another month) at that time. The new one, however, mentions the overstay.
Based on that situation:
1. When they see that overstay entry permit, will it have a negative effect on a new application?
2. On the application form I will answer yes on the question if I have ever overstayed before. Is this answer going to have a negative effect on the new application?
3. Can I apply for a new tourist type so shortly, a few months, after the previous ones? Or are they going to wonder about the reasons?
4. If the new one allows me to stay in China for 30 days, does that mean 30 days including or excluding the days of arrival and departure?
Thanks in advance!