No it does not. It only uses layout additions and observers
There are no known extensions that magecredit is completely incompatible with.
If you're running the eBizMarts SagePay module in combination with magecredit you may run into an issue that calculates the tax settings incorrectly. If you run into this then you will want to disable the credit card surcharges options and everything will be resolved.
Currently no, they cannot choose how much to use. They only have the option to use all their store credit or none of it. This feature is on our roadmap.
This is possible, you can read here on how to create store credit vouchers.
Yes, this is possible.
Read here how store credit can be purchased with real money.
Officially we support any Magento Community Edition 1.7, 1.8 and 1.9 stable version. We plan to continue to support new Magento versions as they come out and plan to support Magento 2.0 as soon as merchants start adopting it seriously.
We considered adding a store credit option to the cart page, however we realized after some user testing that it's actually much more complicated and confusing to your customers than it seems. This is primarily because store credit usage is calculated after shipping and tax information are gathered. This means in order to properly estimate the checkout totals for the customer, you need to already know what shipping is going to cost (shipping address, etc) and tax is going to cost (usually with billing info, etc). Once you have these totals, which you do by the time you are in the billing information step, then customers are given the option to cleanly use their store credit and see the total balance in the next step.
Instead, we added a notification to let customers know that they can later use store credit if they have any. It shows when the shopping cart is accessed for the first time and the customer has store credit. For example, if you perform a refund for a customer and refund their order to store credit (which you can do in Magecredit), then the next time the customer logs into your store and goes to view their cart it will notify them that they have store credit and that they can use that credit in the payment step of the checkout process. That being said, we're actively working on ways to improve the customer process for merchants. If you've got any ideas, we'd love to hear them!
Currently we only support the IWD One Step Checkout extension for Magento. We're working on supporting a few more out the box. If you wish to add your own support it should be relatively intuitive for a developer, provided the one step checkout extension provider developed the module using standard Magento development practices.
Yes you can! Magecredit features functionality that lets you import store credit amounts (to add or reduce from store credit balances) by uploading a CSV file. We've even written some instructions for you on how to import store credit using a CSV here