Hi,
You are correct - if you activate the pass on Mar. 25th, the last say to use it would be at the end of Mar. 31st. A day of usage starts and ends at midnight - so if you activated your pass at 6PM, your first "day" would just be 6 hours.
Unfortunately due to cherry blossom season, many places in Kyoto fill up quickly (or are very pricey). But it is only about 30 minutes by train from Osaka to Kyoto (or less by bullet train, but then you'd have to go to Shin-Osaka to catch it). There is very little between the cities worth seeing however. But be sure you make time to see Nara as well - it is very much worth it.
Regarding getting the voucher, it depends on where in Canada and other factors of course. But typically within 5-7 days. Make sure the address is not just a P.O. box or somewhere; normally a signature is required upon delivery for FedEx type of deliveries.
About how much to spend; there is a lot of variation on personal taste. You can easily see and enjoy Japan on a budget, or splurge if you wish to.
You can eat quite decently for JPY2000 (about $20) for lunch and dinner per day per person. Souvenirs can be a few dollars each to the sky is the limit. If you'd like to see one restaurant guide, see:
http://www.bento.com
But honestly I would not spend too much time looking around for a restaurant, unless it's really someplace special you want to try. Save your time for the best sightseeing places. There are restaurants virtually everywhere and they are almost always tasty and clean.
The other major factor which you didn't mention is transport, not to mention where you will go. If within the same city, if you travel a lot, you can get a day pass in many places for $5-10 or so, at most. Or get a 3 day Tokyo subway pass for 1500 yen if bought outside the city.
http://www.tokyometro.jp/en/ticket/value/travel/index.html#anc03
Kyoto has a bus day pass, but given that you will be in the city at the height of a busy tourist season, taking the subway as much as possible may be wiser. For Kyoto travel, you might have a look here:
http://www.japan-guide.com/e/e2363.html
For other helpful info, see:
http://www.gotokyo.org/en/index.html
http://www.jnto.go.jp/eng/location/regional/tokyo/index.html
http://www.ar.jal.com/world/en/guidetojapan/city_information/tyo/see/akasaka/
http://www.japan-guide.com/e/e2164.html
For Kansai:
http://www.kyoto.travel/
http://www.ar.jal.com/world/en/guidetojapan/city_information/uky/see/central/
http://www.japan-guide.com/e/e2158.html
http://narashikanko.or.jp/en/
http://www.osaka-info.jp/en/
http://www.kansai-japan.net/en/
I hope your trip is spectacular!
