Hey Lucy!
Sorry for the late reply, I'm not around all that much at the moment, but congrats!! Wow, what a great decision.
Okay, some of the things I advise is ask around, talk to any of the previous women the midwives and doulas have supported - see what the word on the street is

There are quite a few websites that support home birthing, they have heaps of info.
As for asking questions, what do you want to know?

Everyone has different things they want to know. Different things will crop up as you go on, so feel free to ask away!
Most of the common questions to ask your potential midwives/doulas -
How do they handle different situations?
What are their transfer rates?
Costs and what that will get you/cover?
In case of transfer, what will happen? Will they support you in hospital/while you need or want them?
What do they cover/not cover - eg. GD, breech, twins, etc
Are they insured? (If they are insured, they may only cover certain situations as in accordance with their insurance compaines rules) Same if they are one of the few who have agreements with hospital/OBs.
Are they hands on or off?
Are they woman-supported or medical-supported?
Do they support your choice of testing or not testing?
Do they perform VEs? Will they discuss why/why not?
Are they available 24/7?
What are their breastfeeding rates like?
Do they supply their own pools if you want one?
What do they supply? My midwife brought towels and sheets, etc.
But mostly - do they
'click' with you?

Take the time to see if you have a good feeling. Its amazing how many women 'know' if their midwife is 'the one'

and which ones aren't!
ETA - lol Krill! Snap!