13's are an extreme for a heavy blues tone. If you want to sound like SRV or Hendrix, that's a start (and not the end).
8's are just too thin. The tone is very lacking, no power in the bottom end. Ya', you can make up for it in the amp, but you just end up with thin tone that's boosted. The only way I would even consider running anything lighter than 10's is for open-C tuning (BadCo).
Stick with the 9's and work up to 10's, which are pretty standard. Hang backstage with many pro bands and 9 out of 10 guitars you pick up will have 10's.
Don't sweat the callouses, they will come with time, but don't over-practice. Heavy playing before your pads are ready will create hard, corn-like callouses that will peel off at the slightest irritation or with a week without playing. Keep it to an hour or less per day for a few months. Within a year, you'll be able to play 10's or 11's without even thinking about it.
As mentioned above... a 12 string acoustic will be a blast!
