CyberGhost, if you are serious about this idea, why don't you contact www.turtlehomes.org
and ask them to teach you about what it takes to become a rescue or foster home for turtles that need rehoming. Please note that it may take them awhile to answer as they just took over an entire reptile museum that was a nightmare of abuse and neglect so they are quite busy these days.
I started working rescue at my grandfather's side when I was 7 so it's never too young to start but it is VERY important to have mentors, financial resources and the proper licensing so you don't end up having the animals confiscated and put in stainless steel dog kennels without heating or UVB. If you're serious about this idea start out very small and slow.
They are one of the organizations that seem most willing to work with new rescues or people wishing to learn the skills necessary to run a rescue. Also, contact your local and national governments to find out what permits are required.
Then, save your money and start sucking up to vets!!!! I spent over $1,200 on one animal in 2002 and the vets are friends of mine who donate their time. That was merely the wholesale cost of medicines and supplies plus lab and MRI fees. You should develop excellent relationships with reptile vets long before you ever take in your first rescue so that you have the help you need. It's a sad fact that there are not enough good reptile vets to go around so it can be very hard to get one on an emergent basis for a newly acquired rescue if you don't have home phone numbers and their permission to call at any hour.
Depending on your local laws you may need to prove you have at least one vet on staff as a consulting medical expert before you take in your first case.