I am trying to start reloading and have now read a couple of books and several U-tube videos. I have just ordered the equipment and will begin to order components. Can anyone suggest a powder that will work in both my .243 and 7mm rem mag

Before you start doing anything, get a reloading manual and READ IT. Usually the first 50 or so pages covers the basic do's and don'ts of handloading and will allow you to proceed safely. Also, to start out, you should really use only load data published in reloading manuals, and always reduce the loads 5-10% and work up slowly unless the load data explicitly states not to reduce the load that much.

As for common powders, I went to ammoguide.com and used the handy powder crossreferencing tool and got the following list of powders common to both the .243 Winchester and 7mm Remington Mag:

1. Accurate AA-3100
2. Accurate AA-MAGPRO
3. Alliant/Hercules Reloder-15
4. Alliant/Hercules Reloder-19
5. Alliant/Hercules Reloder-22
6. Hodgdon H-414
7. Hodgdon H-1000
8. Hodgdon H-4350
9. Hodgdon H-4831
10. Hodgdon H-4831SC
11. Hodgdon Hybrid 100V
12. Hodgdon Retumbo
13. IMR 3031
14. IMR 4007
15. IMR 4064
16. IMR 4198
17. IMR 4227
18. IMR 4320
19. IMR 4350
20. IMR 4831
21. IMR 4895
22. IMR 7828
23. IMR SR-4759
24. Vihtavuori N-160
25. Vihtavuori N-165
26. Vihtavuori N-560
27. Winchester New-WMR
28. Winchester Supreme 780

The issue you might face is that the powder may cross over between the two, but the common powder for a bullet you want to use in the 243 might not be useful for the bullet you'd prefer in the 7mm Mag, but this list gives you an idea of some common powders between the two.

Mike