Saison... Brett?

I've brewed the below saison before and it came out awesome, now I'm thinking I want to sour it with some Brett this time around.

• 8.5 lb Belgian Pilsner
• 1 lb Munich Malt
• 1 lb Caravienna Malt
• 1 oz Amarillo @ 60 min
• .75 oz Amarillo @ 15 min
• .75 oz Amarillo @ 5 min
• French Saison #3711

I know 3711 is notorious for eating a lot, the last time I did the above my beer finished at 1.005, so if I decide to add the Brett to the secondary I'll mash at around 154F this time to leave more for the Brett. I really want the Brett to come through so I'm debating when I should add it.

1. Mash high for 3711, add Brett to secondary
2. Use only Brett and skip the 3711 all together
3. Add Brett and 3711 at the same time in the primary

With option #2, I really have no idea how long the Brett would take to ferment out the full batch.

My last question is around sanitation. If I keg this batch can I no longer use this keg for normal beers?

The Brett won't make it sour. You could use lacto to sour it. There are many ways of going about using lacto (pure culture, sour mash...). If still interested in using Brett, you would probably get more of the typical Brett characteristics by pitching both simultaneously. Time and gravity readings would be your guide of when it's done. I have a separate keg just for Brett and sours. As long as you clean and sanitize properly, you shouldn't have any issues.