Sure, try that. For me when I look very carefully at the buttons for the fighter/bomber/missile corvette, the icons actually stick past the edge of the buttons. I'd be happy with "halfway between their current size and the size of the bonus ships", or just the size of the bonus ships. Then you can use that extra space for the build numbers.
Other comments: It would be nice to have a build progress bar. Maybe not critical for fleetships, but for larger starships (and eventually the Spire) we're gonna want it. Proposal; make the build queue items a bit taller, then have another thing just over the Looping/Running buttons to show build progress. (Could be a percentage number, could be filling that bar from left to right with color).
While I'm critiqueing things, the for the Fuel Synthesizer/Aux reactor etc, the flairs are weird. Fuel is blue there but a kinda a light pinkish in the resource bar. The "power" icon looks really fuzzy and sometimes the lightning bolt is going to the left and sometimes the right. And metal is purple instead of pink.
Also it would be nice to have the mark levels in the sidebar made larger. Also, is there any rhyme or reason to the ordering of ships in the sidebar? In one of my modded games the icons golike this.
First row: Laser Gatling Mk 1, Autocannon Mk 1, Laser Gatling Mk 2, Laser Gatling Mk 3, Spider Mk 1, Autocannon Mk 2, Fighter Mk 1