Recommendations to generate a training set of images
1) wouldn't recommend switching cameras, could consider some type of resolution mapping to help though.
2) Likely not, but resolution alterations likely would.
3) Deeplearning => require more data, use transfer learning so you can use a less though.
4) try to keep the data as similar to it would be in production and try to keep the images general to avoid bias. (example: image recognizer predicting any image w snow to be a wolf)