I've had ASUS motherboards that have been "fussy" about RAM but only when it comes to dual-channel operation.
They do generally have an "approved" list (I think there was a reference to that via one of the motherboard links above) if you really want that to work, otherwise I've just used more generic modules of an acceptable specification and run single-channel.
I think the "approval" is down to detailed timings of the ram - latency etc. see
https://en.wikipedia.org/wiki/Memory_timings My main W10 PC (typing this on it) has 8GB ram and is using about 2.8GB when not doing much, so I guess 3GB is going to be a bit tight and involve a fair bit of paging.
I generally try to follow the old 70% rule on real memory, so I would probably get away with 4GB. The analogy I use is fitting furniture into an office and changing the layout; if it's covering 70% of the floor space it's getting really difficult to move it around!