Even if you are using a pruned node, the first time you boot it you must sync the entire blockchain, then close your client and start in pruned mode
You can start in pruned mode since day one. You don't have to store it at all.
if you copy the files it is still a really slow process.
The software will not do any validation after you copy the files to a new storage drive. It's not aware of the drive change.
And do segwit blocks actually make blocks higher? I thought the blocks would still be 1MB, but they can fill up to 4MB worth of transactions.
Old client software will only download 1MB per block, but new SegWit-aware clients will download the full SegWit block data, which can potentially be more than 1MB. The estimated figures I saw for a practical size were about 2MB or a bit more. It might be technically possible to create 4MB SegWit blocks, but what I read suggests it won't be useful for transactions of the type the network is currently used for.
I don't get why would anyone want to use an SSD for the Blockchain. It's just a waste of money since you're just synchronizing it once.
The blocks are less of an issue. The UTXO set is, at least with the
inefficient disk access patterns of the current version of Core. It might be related to using pruned mode, but I get the feeling the disk I/O inefficiencies go beyond that. If the issues are fixed, I think indeed HDDs will suffice.
SSD might be slightly less unreliable than traditional HDD, if there is too much write and read operations.
I don't think there's enough writing to matter to SSDs, but I haven't checked. Reads don't matter.