Don't worry, anyway there is too much articles related to this project over the years. So lot to read.
1. If all goes as planned with HDMI you will have much, much more
2. For start you will be able to use SCART + HDMI in the same time, however plan is to get everything over HDMI(old games, workbench...) so nothing else will be needed + FPGA will eventually provide GPU...
3. Nothing needs to be removed
4. Original power supply is enough since this time, unlike on old version we solved power supply for the card another way, you have article on that on my site.
Goal now is to provide ppl cards who are capable of any kind of upgrade in the future.