Should I include p-values in a Census type data?

Hello guys,

I am conducting a study that compares rates of CIF (Client Intake Forms) completion collected among via self-administered paper-based interviews (SAPI) as compared to electronic collection via iPads. By completion I mean CIF that have no missing values, that is all questions were answered in the CIF. I am using data of 26 centers. These centers administered the CIF in the two modalities - paper and ipad. The CIF is administer to every single client that appear at the centers. (8000 clients). In total, 70% of CIFs were administered via paper and 30% via iPAd. I have two questions:

1. Should I include in my manuscript p-values? I believe that my data is not a sample because all clients were included. I believe it is more like a census type of data. when I run test of significances, everything is significant even small differences since my sample is huge.

2. Although all center have the two option modalities (paper CIF or ipad), some centers only use on modality. For example center1 have 100 CIFs via the paper and 0 CIFs via iPad. Is this a problem? will this affect my results and the validity of my study?
2.1 Also some centers, have very low client volume- i.e. only 3 CIFs. Should I exclude center with low CIF volume like my example. If so, what would be the rationale?

I think that the problem is that were not randomly assigned to one of the other modality.

Any thoughts?