I would focus on the 8GB/256GB Mac mini and then just upgrade again in 2-4 years. $499 edu is no joke, and Apple’s extra 8GB for $180 is insane. All the YouTube/etc. videos show people perfectly happy with 8GB of RAM.
This “half the speed, 256GB vs 512GB” is absurd. In a black magic benchmark, sure, there’s a difference. Otherwise, there isn’t. Most can’t even tell the difference between a fast NVME SSD and a decent old SATA SSD (at half to 1/3 the “crippled it’s so slow!” 256GB Mac SSD speeds).
Don’t buy the hype. Get a basic Mac mini, be happy, use it for a few years, dump it, and upgrade when there’s something significantly better. What’s out right now isn’t. Yes, it’s more cores, but unless you have an app that can actually use those ‘more cores’, they’re wasted. Wait for something that significantly improves the per core speed because that’s what you will feel in everyday use.
The direct answer to your question about Apple and OS support: Apple supports their stuff for about 7 years after release. Whether you buy 8GB or 16GB, I wouldn’t worry about that. You’ll get a long product life, and you can easily sell, lose very little money (because you’re spending very little money) and get something better in a few years.
Save your $.