1. Since you're visa-exempt, you can apply for the work permit on entry into Canada, or in advance. On entry is faster if you need to leave for Canada soon after the marriage, as you won't have to wait for the embassy to reply, you'd do it all at the border when you get here. You should make sure you have all the necessary documentation with you (proof of your marriage, and your spouses work permit).
That said, if you're not leaving for a month after the marriage, getting the work permit up front gives you the confidence you're "pre approved" so won't have any problems when arriving in Canada. (It should be fine to apply on entry, but you could choose to do it in advance.)
2. No need to pay for a lawyer for a simple work permit.
3. Through London, 3/4 applications are processed in under a month:http://www.cic.gc.ca/english/information/times/international/15-temp-workers.asp#europe
If you apply on entry, it's just a delay when you arrive, maybe 20 mins while they process it at immigration secondary.