1/4" might be a bit much I usually cut mine 1/8" shy but if you are using 1/4" acrylic you should be ok.
Cut yourself some strips of acrylic the same height as the baffles (depending on the flow through your sump they should be 1"-1.5" wide) these we'll call gussets.
Now apply a nice bead to two of the gussets and press them firmly flat against the glass at your starting point. Next a baffle, then a pair of "gussets" to sandwich it in place and so on.
This technique will keep the spacing nice and even and also allow the baffle to "float" between the gussets during expansion and contraction.
A couple of tricks I've picked up:
>Work from the end of the tank to the middle.
>add and wipe a nice silicone bead to each baffle as you go (you won't be able to reach it later)
>Use a sharpie and mark yourself a layout on the outside of the tank before starting (some water and a razor will take it right off after)
>on the bottom side of the baffles use a sanding block or random orbit to round the corners to relieve where it contacts the existing silicone bead in the tank, this will make the baffle sit flush to the bottom of the tank.
>Instead of trying to prop up and space the baffle for the "under" flow, just cut it to look like the bottom of an H leaving ~1" "legs" and the same 1"-1.5" as the strips space from the bottom for flow under. This way you can set it right in without messing with propping it up etc.
hope some of that made sense
