I already have ~145 GB of the blockchain synched on a HDD but the rest is very slow to synch. How can I download the remaining on my local hard drive then move it over to the 1 TB HDD?
What I'll do is to synchronize the client completely on a normal computer and then transfer the entire data directory to the HDD. It'll save a lot of time as you can validate faster on the computer due to its better processor.
That's true but even if you use it 24/7 it's going to take years before the disk degrades. It should survive at least 3 years of heavy load.
Blockchain requires over 300 GB, a cheap 512GB SSD will cost you about 50EUR. It's the average price of a computer game

I don't think anyone actually did an actual test on it but a good priced SSD should withstand the degradation pretty well.
The first node launched by me was relied on Intel SSD 320 Series 120 GB bought in 2011 and that SSD is still alive. Now it utilizes Samsung 860EVO Pr0 1TB. I bought it with plenty of GB to last up to 2025. When choosing its size I was using calculations done by ETFbitcoin