Due to budget constraint, the only difference for both builds is just the casing (either mATX or ATX), this is because ATX mobo will cost you another RM 200 (more or less).

Intel Core i5 6402P - RM 767
ASRock B150M-HDV - RM 283
Corsair 8GB DDR4 2133MHz Value RAM - RM 238
Gigabyte GTX1060 6GB GDDR5 Windforce - RM 1269
<SSD reuse>
Seagate Barracuda 1TB HDD - RM 205
FSP Hexa+ 550W - RM 188
Segotep Gank II - RM 179

Total: RM 3129 (ETech price inclusive of GST)

Not sure if you need a new HDD or not, if don't need, please remove it and the total cost will be within your budget.

1. Both mobo are running a similar chipset (B150), so please expect the features offered by each of them will be almost the same apart from few extra I/O ports from the more expensive one. MSI B150M Pro-VDH comes with 4 RAM slots (vs 2 on ASRock), 1 SATAe port (not really that important and useful nowadays), USB 3.1 (vs 3.0 on ASRock, but 3.1 adoption rate is pretty low currently) and so on. NVMe M.2 SSD is not supported by both of them, if you plan to get a speedy next gen NVMe M.2 SSD then you might need to consider other mobo (this will increase the total cost needed but more future proof).

2. Yes you can do so but you need to top up for it.

3. Yes you can do so too but the RAM speed will be downclocked to 2133MHz automatically due to the nature of B150 chipset, only Z170 can support RAM speed > 2133MHz.

4. 550W is more than enough, power consumption of the new hardware is getting lower and lower now.

5. Tecware F3 is a mATX casing whereas Segotep Gank II is a ATX casing, if you don't plan to reuse the casing for future mobo upgrade (to ATX mobo) then F3 is fine.

i doubt u will actually find any different in terms of gaming for both monitor. my friends use the Acer one and i think it looks great but the monitor is glossy and some people dont really like that.

aesthetically the Acer looks better too since it have that bezzless design.

VA and IPS, both are having almost similar response time (4ms for Acer's IPS and 5ms for BenQ's VA), I doubt you will see any difference. RM 450 can mostly get entry level 1080p 60Hz monitor, TN panel will be the best option if you want lowest response time among all the panels type available.