mosaic is a soft, fruity hop.
to keep things simple, id suggest a grain bill of 94% 2 row and 6% crystal 40 or 60. mosaic is hop that does really well with medium crystal malt.
for 6 gallons post boil @ 75% efficiency (easy 5 gallons in the keg or bottle) go with:
11lbs 2 row (replace with 7lbs DME for extract)
.75 lbs C60
2.5oz of aroma hops @ 0 (steep for 20 minutes)
2.5oz of aroma hops for dry hops
to step the game up even more - pair that mosaic with something citrusy like citra, amarillo or centennial. or all of those if you have them.
us-05 is always a classic APA yeast, but you could us s-04 or wyeast 1968 if you want a softer, maltier brew.
good luck!