masshi, the argument you'll hear here about getting jeans tailored is that, unless you take it to one of those jeans places in NYC that get mentioned sometimes here, places i can't remember the name of right now, you'll be straying from the quality construction of the jeans as well as the original intent of the jeans.
these jeans are created on vintage equipment with the highest of care, and a tailor is in a cost-cutting, "get it done fast" business that doesn't take the time your jeans got when being made. You will be straying from the strong quality construction of the jean. Jeans, in the top block, are a complicated bunch of connected parts, and slimming that down might mean taking it all apart, and you can't guarantee that your tailor is gonna make it look like it did in terms of stitching, details, and construction when they're finished.
Also, jeans like the ones from Self Edge are focused around the ideal of reproductions of classic jeans, and having a tailor get involved, with their modern equipment means breaking away from the reproduction ideal.
If you care about that stuff, well, you sound you belong on SF. If you don't care about that stuff, risk using your tailor.
As to your fit, the top block on those looks way too large, yes, including the waist, and yet is somehow riding all up your ass at the same time. though you don't look like you have the buttons actually buttoned up, i doubt that changes much. the legs looks great, btw, except for the goofy standing-on-the-hems bit. You are, indeed, very, very skinny.
I'd say sell 'em on B&S and get something else.