Hi there.
As Bob sayed you can go with internal drives and use lets say ProRez an you will be fine. I use my 3 internal 1 TB drives and can do a bit uncompressed but my jobs are short 30 sec or so. My drives are pretty empty also. For longer movie etc external boxes are must if you do not do all your stuff ProRez.
Of course one can play trics and install 4 x 2tb drives etc but this is not something for common user and there is alot warranty questions etc. So go just for 3×1 tb drives and you will be fine.
For CPU i’d say deffinetly 8 cores and as fast as you can pay.
Maybe it is not most reasonable way but it keeps your machine running a bit longer in years to come.
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Margus
https://iconstudios.eu