Do I get an M4 Pro MacBook Pro with 512 storage or a standard M4 MacBook Pro with 1TB?
What’s more useful for the long term in your opinion?
I would get the better Pro CPU vs 1 TB storage. 512gb storage is enough. Cloud storage isn't pretty nor is external drive but it can be managed and cheaply. The CPU is the CPU for as long as you own the laptop. Might as well have a better model CPU if you are using it for Pro uses.
You say you do video editing and music recording I think the Pro CPU would be beneficial for both.
I would probably suggest you spend the extra money on the 1 tb drive too. Just pay for it. But keep it for at least 5 years and it will make more sense. You can't future proof anything but you can make sure that your experience while you have your device is good the entire time you own it. If I can get 5-10 years out of a device and it doesn't become a slow glitching mess by the last few years then it is a winner. I expect 5 and am happily surprised if I get more. So if you pay more but then because you spent more and got a better CPU/GPU and larger SSD now you don't need an external ssd and as time goes on your laptop doesn't miss a beat. It may be that you are ready to sell it before it slows down on you which would be ideal but still served you 5 or 6 years.
Just looking at specs and money is hard. We never have enough money for the specs we want. I think if I were going to buy a Pro laptop I would get at least a Pro CPU, 32gb ram, 1tb ssd or better depending on my use case.
If it is just a personal computer and I want the better screen, ports, etc, then the regular m4, 512gb ssd and 16gb ram would be more than enough. If I were in the market for a new laptop a 14" M4 MBP with these base level specs would be pretty nice.
Once you use an air though it is hard to go back to a "Pro" model despite all the extra's. There is just something about a well designed laptop in that sweet spot of not too small and not too big. No fans....I digress.
Honestly only you know what is more important for what you do. Is more SSD more important or is a better CPU/GPU more important. Most people who want a "Pro" machine value performance over other things and so my inclination with your question is to say a better CPU has better performance which is the entire point of the "Pro" but that is in my mind and not yours so I don't know what is more useful. I Know which I would choose.
Just to add I have had experience with m1 when it first came out and m2. I have owned a lot of laptops over the years and no matter the maker or OS after a year I generally replace them because performance degrades rapidly after that first year. Re-Installing the OS may help and it may not. Some laptops last about 3 years if I am lucky and most go after the 1 or 2 year mark. This tiny M2 MBA has now been with me over 3 years and hasn't skipped a beat. A feat I must admit I never thought would be possible until now. I am pretty sure it will go another 3 easily and possibly longer. Without the annoying lags and slow downs you get with Intel based Macs and Windows laptops but since M series chips just doesn't seem to happen. I noticed the m1 feel a little slow but that was after 2 years or more.
What I am saying is since everything is a one shot deal with m series in that you can't add ram or storage later theoretically. This new architecture being on arm and just much faster chips means that there is so much more headroom in the OS for performance than in the past. My Windows laptops will be spinning up fans while do nothing and at the same time my air is silent doing a ton of work?
If you have an M1 or older laptop/desktop then this is going to be a big change and in my experience is not like Intel or PowerPC at all. You may be able to buy whatever your configuration is going to be and it may last you longer than you expect and perform better while you use it until you pass it along. So it might be wiser to spend a little not a lot as I am no fan of future proofing but being realistic about what your needs are and buying for now. What will will work best now and gives you enough headroom now that you can perform well. If 512gb SSD is more than enough for now with what you do then just buy that. It is plenty. If 1 tb is what you need now for the work you are doing then get it. Same goes with the CPU. For the work you are doing the Pro CPU will make a significant difference. Having as much ram as you can afford now is also important. I think for "Pro" needs 32gb ram is the optimal for most users. I think 512gb and up SSD is optimal for most people. Unless I am buying a pro just for the screen, speakers and not for performance then the regular m4 would not be recommended. So an M4 Pro, 32gb ram, 512gb ssd (min), and whatever config else you want. It will last you a long time and perform well. I would suggest most people try an air but for your use case you do not seem like one of them so I won't even go there.