You would be starting out on a new Mac with the primary drive 60% full. That seems inadvisable, unless you don't anticipate adding anything significant over the next 5 years or so, the typical life of a computer. But if you plan to use it for 15 years like you did with your 2010 Mac (which is commendable!), then I absolutely would get much more storage built in. Typically storage needs grow because of: email that is stored on the Mac, especially email with attachments; photos/images; music; Messages (with attachments); or various "projects" which might have associated powerpoint or Word files, videos, etc. Video work tends to take up a lot of storage. Use of software like Adobe Lightroom can use up huge amounts of storage temporarily as it takes up a lot of scratch space when your Lightroom catalog has lots of image files. In the future, cameras will be producing much larger jpg and raw files, those will take more storage.
Note that Apple offers several iCloud options to offload some or all the above from your Mac's internal storage. If you are willing to adopt that lifestyle, you can keep local storage to a minimum.
Personally, I used to have a 1 TB minimum internal storage and now am going for 2 TB minimum.
For external drives to backup to, you can look on large resellers like Amazon for external drives that have 4.5 or more stars from tens of thousands of users, and also products where the manufacturer offers 5 years warranty (or at least 3 years). Actually exercising the warranty is more hassle than it is worth, in my view, because the cost recovery gets eaten up by shipping costs, etc. But the longer the warranty, the more the manufacturer believes it is higher reliability. There are many manufacturers, these device are mass produced by the millions and many of the different brands actually share the sam drive mechanism.
I think the real question for you on the external drive is whether to go with SSD or HDD (mechanical). The SSDs will typically be 500-2000 MB/s, versus ~ 150 MB/s for an HDD (mechanical). But the mechanical HDD will cost maybe half the cost of an SSD. SSDs are more rugged and have no moving parts to wear out. They are believed to be more durable and reliable. Again, look at the ratings where there are many customers reporting back. For a small business, a family member has used about 50 external HDDs and 2 have failed, which is in line with the industry norms of ~ 5%. We have used about 10 SSDs and none have failed, but some of those HDDs are over 15 years old, the SSDs are all fairly new. You can make yourself largely immune to failure of these external drives by having two Time Machine backup drives -- Time Machine alternates between them, this covers you in the event of failure of your computer and/or one of the backups.