That should be about correct, as our WP85xx actually seems to have 150MB available for the apps core and with the default set of applications there is still ~60MB available.
This also includes the kernel and non-Legato processes, so the framework + default apps by itself takes way less than the used 90MB, altough I wouldn’t be able to give you an exact number.
As for ROM, the framework as squashfs (so, compressed) takes 2.6MB. Uncompressed it’s about 3MB.
It does require a minimal Linux to work on though, so you would need a Linux kernel and busybox, and as for now it also requires a ‘workspace’ where it can extract itself and run from, altough we are making that optional by making a ‘read-only’ mode available, But still, overall a working Legato can likely be ported to a system that has less than 64MB of ROM without too much trouble.