My first labour was 24 hours, 12 hours in pushing stage, so I get you on the exhaustion thing!

My suggestions are:

Birth at home.
Make very very sure you are well hydrated.
Electrolyte drinks can be good to help make sure you are not sweating all of your salts out. ( I made a special recipe called 'labourade')
Eat during labour to keep energy levels up
Honey can be a great pick me up
Labour in water, it can help with relaxation
Practise relaxation techniques

All the very best, I too was worried about a long gruelling labour second time around, and it was 4 hours! The mw almost didn't make it!

After birth I took liquid chlorophyll a few capfulls a day as I also lost a lot of blood, and could only crawl around the first few days! (I should have been in bed, but that after birth high...)
I also took Floradix to help boost Iron stores.