Will recommend the TP-Link Archer C7 v4: https://www.lazada.com.my/tp-link-ac1750-wi...is-1774185.html or the ASUS RT-AC1300UHP.
I agree with you on Mikrotik. But, getting the ASUS AC86u from Taobao is risky, as ASUS Malaysia will not cover your warranty if there is any problems with your unit if you buy it from overseas. Just something to keep in mind,
I agree with you bro. I am still learning about networking in general and configuring Mikrotik as a router as well. No point getting something if you can’t really use it to its full potential.

Just some more information:

Usually different countries have different laws on wireless frequency transmission - it's best not to import a router from other countries as the underlying firmware may transmit wireless signals at frequencies that may be forbidden here

Also the router from Taobao may have a different firmware (which may have a backdoor installed, due to government regulations) in it instead of the international firmware 

Pòssible yr rtn12hp about to die.

From yr description, i recommend u the rtac1300uhp... it will be better than rtn12hp or stock router.

More so for devices than have dual band, can easily get better wifi speed if not too far using 5ghz freq.

It is also good when u go 100mbps.

There are surely better routers but will be more expensive.

And for 50mbps, i will certainly not spend more than rm5xx.

I would recommend the TP Link AC350 v2 if you are intending to pay RM750 for the AC87U. The TP Link is newer and have nearly same features as the AC87U plus your house is only double storey. See here: https://www.lazada.com.my/tp-link-archer-c3...81e5NFJvLR&mp=1

Or you can get the ASUS Rt-AC1300UHP, which only goes for  RM5xx. That should be sufficient for your needs.