1) I have Schwalbe Marathon Plus tires on both my commute bike and my utility bike - between the two bikes I have 25,000 miles and 2 flats.
2) Teach the toddler to change tubes . If you have good tires, you probably won't ever get to watch Jr changing a tire.
3) Personal preference, but for heavy bikes (and all my bikes are heavy), I like frame locks like the ABUS with an attaching chain. Easy to carry, always there,
4) Can't help you on that - I'm a trailer guy, and my trailer converts between cargo and kid modes.