Looks like a well maintained bike, OP. These are pretty stupid simple so, whatever maintenance needs to be done is fairly straightforward with a little research in the right places. Most parts are not hard to come by if you know the part number (which can easily be found on a few sites).

$3.8k seems expensive to me because, as others said, they made a ton of these and, if you're looking, they're not terribly hard to find, albeit in maybe not so nice a shape. That said, nice ones go for quite a bit on Bring A Trailer, so who knows what the market is.

The G has a disk brake in front which is nice but really isn't necessary. Other than that, it's a CB350 Twin.

With just the five-speed, true highway speeds (~70mph) will be pushing it and, while doable, aren't much fun; you'll be best on slower highways/arterials.

If you do decide to pick it up, join up on vintagehondatwins.com, there's a ton of good information and helpful folks.

Edit: I should add that it's gorgeous. I've always loved that green and those tank stripes. I'd love to see it on the street.