I don't have a donkey, but a mini mule. I think donkeys are easier LOL! But they are different than horses. You can usually bully or cajole a horse into doing what you want, but a donkey is very sensitive and won't do something it's not sure of unless you convince it that's what it wants. You need infinite patience to train them.
Gaining your donkeys trust, bonding and ground manners are the most important things before cart training can start.
The only advice I can offer is to keep reading and doing research. The Merideth Hodges books and website are a great scource of info. I wouldn't bother with the training DVDs, I bought one and it had the same info as the books. Wasted $50. Merideth does answer your questions tho, You can always contact her through her website.
Good Luck!