If the BB that's on the bike now is 110mm (as I think you said above), I'd mount the new crank on it before buying a new BB to see what kind of chainline you end up with. Best on a 1x to have the chainring line up with the middle cog on the cassette. Another spindle length might work better for that [I think the 103, 110 marking on the Sugino crank probably indicates a recommended range, depending on rear hub spacing (eg, 126, 130, 135) and frame design]. You can move the crank inboard to adjust chainline with a shorter spindle, so long as the chainring clears your chainstay (a smaller chainring allows the crank to be mounted further inboard and still clear). Even with perfect chainline, you may have problems keeping your chain from jumping off the crank with a 1x, where it might stay in place on a single speed with a less than perfect chainline. I converted a 2x9 to 1x9, then 1x7 because it's easier to shift with the friction shifter I wanted to use. My chainline is close to perfect, but the chain would occasionally jump off, so I installed a chain keeper (not a chainguard, which only keeps your trouser legs out of the works). It all works perfectly now. My rear hub spacing is 135 and my BB 68x107, btw. I'm running 39x13-28, and can manage 12mph at a knee-saving pace with that setup, plus I've got the gear range for some decent hills. I have a 42t chainring in my parts box as well, but I'm happy with 39t for now. Don't think I'll ever need to go as big as 48t, but then I'm 59 and maybe not as ambitious as I once was.
