:D Don't do as I say, @phoenixwren, but with that amount of excess I would just cut off half. My main reasoning is that it would take too long to dry when washed - I don't have a drier so I try to minimise 'natural' drying time.

To stop it unravelling I would leave just an inch (2.5cm) seam allowance and just do blanket stitch to stop the fraying / unravelling sort of mimicking the serger / overlocker effect.

If it's a t-shirt I do find that it stretches quite a bit so I'd refrain from 'hand sewing' too much.

Do you have access to a sewing machine with zig zag stitch ? For internal 'side' seams I would use that if needed (often it's not).

My biggest issue is shortening lengths as I'm vertically challenged (short :D).

I have used hemming tape. So I fold the hem to the length I need; cut about an inch from the fold; apply the hemming tape; and then sew straight. It makes it look nice, but it will depend on the quality of the jersey ...
I found a video to show you what I mean.