You’re right, SATA isn’t going anywhere for a very long time. If you have a need for 4+ TB of total storage there is nothing at all wrong using HDDs or 2.5" SSDs.

Same here (northern Midwest US) for new construction. Although, to clarify, they’re still generally routed/ducted through the attic and exit through an exterior wall.

Unfortunately since these are single pane windows most of the thermal performance issues will be due to the glass. Sealing this gap will help some, but it will be just a drop in the bucket.

Replacing the windows with insulated glass (two pane) windows is ideal. However that will be expensive.

The easiest/cheapest option will be the temporary cling-film type kits you can buy–you won’t be able to operate the windows, but that probably won’t be an issue in the winter. Properly sized/installed storm windows will help some too, and be significantly cheaper than new windows.

It’s a bit hard to tell in the pictures: is this a dual pane vinyl sliding window?

If it’s single pane (or single pane with a storm window) there isn’t a ton you can do. Most of the sound (and cold) will be coming though the glass. Anything you add will have a marginal improvement.

Assuming this is dual pane, there probably aren’t many place you’d be able to add weatherstrip that don’t already have some. So replacing any crushed/worn weatherstrip is one of the best things you could do.

Have you pinpointed exactly where drafts are coming through? You can use a candle/lighter to see where air is intruding. Oftentimes drafts are due to poor installation, and not necessarily the window construction.

Is this picture from the exterior? I’m guessing this is a fixed vinyl (as opposed to wood) window?

If it’s the exterior, that gap might be for water drainage. If it’s the interior it might be for equalizing interior and exterior pressure. I’m doubtful either is the case though.

Filling the gap is likely okay.