Mate, it doesn't really matter if you push LOC first or not, but you don't have to. If you push APPR you get LOC and G/S in blue underneath whatever are your active modes (probably ALT and HEADING in your case), meaning both are armed. The airbus manual says "The pilot arms the (ILS) APPR mode (LOC and G/S in blue on the FMA) by pushing the APPR pushbutton on the FCU" [FCOM 1.22.30.51]
Flightsim is not the real world, and is based on American r/t. In the UK it used to be standard to be cleared onto the localiser first, report established, then get cleared on the glideslope. This now thankfully has changed so you can descend once established without having to report it.
The reasons being are historical, but I believe someone once descended on the glideslope without being established on the localiser and probably flew into high ground.
Occasionally, mostly at airports with parallel runways, you can still get cleared for the localiser first. This is because if you started to descend you might trigger a TCAS event.
So for these reasons, for me personally, if I am only cleared on the localiser I just push LOC. If I am cleared for the approach I push APPR. Other people, when cleared for just the localiser but are expecting the glideslope later, will push APPR straight away.
Both ways are correct and ultimately it's not worth arguing over whether you push one or two buttons!