Well you can always add external/cloud storage...
but bear in mind that you really don't want to have your
system drive ever get too close to being full - drives slow down as they fill up, particularly SSDs, and a slow system drive will slow down the writing of temporary files, virtual memory etc. and drag down the whole system. If you google it you'll get advice ranging from "don't worry - the OS will enforce a minimum amount of free space to prevent total gridlock" (probably true) to "never exceed 50% capacity" (probably exaggerated). However, if you're getting close to 50% full
on day one then I'd be worried. Also, on a
laptop it makes a huge difference to have all the files you need on the internal drive without having to plug in externals or worry about internet connections on the road - plugging in external drives and/or a reliable internet connection on the desktop isn't such a problem),
256GB is probably enough for the sort of use you describe - but if you're using "Pro" apps (FCP, Logic, XCode, full-blown Adobe CS) which can need lots of space to install, are using virtual machines at all, or messing with video editing, I'd go with 512GB or 1TB. On some Mac models, larger SSDs can be
faster too. Personally, I'd say that most people should be able to work within 512GB, 1 TB is a convenience and going over 1TB is overkill
unless you know a specific reason why you'll want more.
I think what I'm saying is that I'd probably go to 512GB storage (and probably 1TB on a laptop) before 32GB RAM if I couldn't stretch to both.
As for RAM, unless you know you have individual jobs with huge RAM requirements, 16GB RAM will be enough for most things in the near future - and not having more is unlikely to stop you in your tracks in the future: maybe things will slow down a bit, or you'll have to get better at quitting apps that you're not using, using bookmarks instead of browser tabs etc.
OTOH, if I were buying anything other than a Mac for anything other than "Internet & productivity", I wouldn't even bother with less than 32GB & 1TB - Apple under-spec their Pro machines and charge usurious rates for upgrades, and we shouldn't really have to be making these decisions about what are relatively modest base specs (32GB/1TB) for a "pro" laptop. So it partly comes down to "do you like Macs enough to stump up the 'Apple Tax'". I was at the end of that tether with Intel "PC clones with nicer touchpads" Macs but Apple Silicon has refreshed my interest a bit. At least they're now using LPDDR RAM (which can't easily be made user-upgradeable) and mounting it on the package for performance reasons - not just to stop upgrades.
I wouldn't
plan on keeping a computer for 7 years. Hope, maybe - my 2011 MacBook Pro was my main work machine until 2018 (However, I think the longevity of the ~2010/11 Macs was mostly down to the ease of replacing the HDD for an SSD which
really made them feel like a new machine). I'd
plan for 3-4 years and regard anything beyond that as a bonus. Remember that, by 5 years, they'll be well behind on CPU/GPU speed, won't have Thunderbolt 6 or Multiversal Serial Bus 5.2.1gen2x42superPlus ports retinaID sensors - and might not be supported by the latest MacOS or applications. They'll still do what they do today, but you'll be making a load of other compromises beyond closing a few browser tabs.
One "thinking tool" that may help is to divide the cost of the computer by the planned lifetime (say 4 years) then asking how many extra years each upgrade would have to buy you to be worthwhile.
So, a $2000 14" MBP over 4 years would be $500/year - in which case, if you think a $400 RAM upgrade stands a good chance of extending that life to 5 years it seems like a reasonable deal.
