Absolutely go with SSD. As others have said, the price premium between a tiny 128 gig ssd and even a 1 tb ssd is comparatively tiny these days so I’d recommend going with at least 500 gigs. A m.2 PCIe ssd (i.e. small and flat) is also much faster than a 2.5’ SATA (large and boxy) ssd and the price premium is negligible these days, but make sure your motherboard has an m.2 slot - most recent cpu platforms should have one.
If you live in a country where websites such as Amazon deliver, I would recommend going to PCPartpickers and sorting through the options by price/gig (here is an example of my parameters – https://pcpartpicker.com/products/internal-hard-drive/#t=0&sort=ppgb&page=1).
At time of writing the best priced SSD seems to be the M450 1 tb for 25 USD, which is a ridiculous sale that I would personally jump on. (it is an m.2 so see above note).
Hard drives are only really good for cheap mass storage (e.g. if you have literal mountains of photoshop projects) and servers these days (e.g. those 6 or 14 tb disks from seagate), or if you’re building a computer out of literal trash with scavenged hard drives in which case i would refrain from saving anything important on them.
Even though there are lots of vendors, most SSD components are sourced from just a few companies: the NAND is from SK Hynix/Micron etc., and the controller is from Silicon Motion/Phison etc. Some of the larger vendors (Intel, Samsung, Crucial, Hynix, WD) produce their components in-house and are also more reputable, but the actual differences most of the time are minuscule. I would recommend purchasing from one of those vendors, but at lower price points (e.g. Intel’s 670p or Crucial’s P3) they often use cheaper QLC NAND which throttle the sustained write speeds when copying lots of files, and also have lower endurance. Laptop users generally don’t have a problem with these if all they need is snappy-enough everyday use, but professional users (e.g. copying tons of photos) might lose time or reliability depending on their use case. If I’m penny-clinching, I would recommend picking out the cheapest drives with the characteristics you desire (e.g. pcie generation and capacity), then doing your research as to componentry. If I wasn’t trying to save every last penny right now, I would probably get the Crucial P5 Plus 1TB because it’s from a reputable brand and a noticeable improvement over cheaper drives ($49). At higher capacities, I’d be more inclined to simply get the best of the best considering how cheap the (gen 4) prices are right now, or at least close to it such as with the samsung 980 pro 2TB.
For motherboards, having an m.2 slot is probably not an issue if you’re buying new. my advice would be to pick a chipset that supports the cpu you want (e.g. z790/b760 for intel’s latest, x670/b650 for am5), then sort by price while looking for the other qualities you might want first (e.g. overclocking, xmp, onboard wifi, networking, decent onboard audio). speaking of motherboards, what cpu do you think you’ll get?
I’m not qualified to speak on redundancy or backups.