corporate-wage-slave

If you are doing this the same day, you face an enormous risk if there is a weather event or some such. Back to back flights mitigate this risk but are impossible with checked baggage. I would therefore urge you to either go the day before (at least on the first set of flights, last set is less of an issue) or split off the Paris sectors from the YYZ sector - which costs a bit more APD but makes it much easier to do.

But to answer the questions, your wife can go through connections so long as you don't exceed your personal allowance. If you are using her allowance too then you both need to be there.

1) Yes, you collect bags and go landside to check in, then back through passports and security.

2) You should be able to get all the boarding passes, and thus get lounge access in London, however make sure you make it clear you are heading to Paris first since you don't want to start conformance to YYZ before getting to Paris. So show the BPs, don't let them scan it.

3) Yes, bags can be through checked from Paris. The alternative is to leave them in the paid for left luggage office in T5, and collect them, check them in at T5 after
Paris, thus reducing some of the problems with the Paris trip.

4) Unless you have status, I don't see how you get lounge access on the final flight from Paris to London after your visit to Canada, unless you are travelling in Club of course.

It is sometimes better to look at fares from NCE and LYS rather than Paris, they are often about the same but it is easier to deal with these airports compared to Roissy.