No. GSM was integrated into the OPL EE core. OPL is still operating, even if you use this GSM.
In contrast, POPS is run instead of OPL if you use that POPStarter integration.
If you actually want a stable release, get the stable release. Don't get those nightly builds (Or the thing branded as "Daily Builds"). You should read
this link to understand what those terms really mean.
Long ago, we used to just release OPL from a thread on psx-scene. I also created a thread here. Now, I don't know how it's done.
But I'm sure you know how to Google for it? It's OPL v0.9.3.
I don't know if they made a new release. Shortly after I stopped working on OPL, OPL v0.9.3 was released in 2015.
After that, there were many commits made, but no actual releases. If one builds a copy of OPL from these versions, there could be new features and bug fixes, but it doesn't mean that it is of good quality.
You mentioned HDD, so I thought you could use one. But for a slim console, it's not usually an option.
If you can afford the space, don't waste time with hacking up a game. You might find it to be time-consuming.
I don't know, as I've never used IRISMAN. But PS and PS2 games on the PS3 are emulated. When something is emulated, there is a potential for the emulator to enhance the graphics during the rendering process. I know that PCSX2 allows for this. If it's not a choice for the standard PS3 firmware (I don't recall it), you should check the documentation for IRISMAN to understand what it really does.
Like I mentioned before, GSM doesn't actually increase the quality of graphics. Only the video mode gets changed. Even if you selected one that has a higher resolution, the game's frame buffer is actually magnified.
This is an area which differs between the PS2 and PS3. In the PS3, the PS and PS2 are emulated, and the video mode can be changed.
Playing a PS game on the PS2 probably results in the same video signal as when the game is played on a real PS (game can also control whether it's non-interlaced or not, from what I rememeber). Even though the PS GPU is emulated in software and Sony would perhaps have a choice to change the video mode. I suppose it was just an acceptable design, 20 years ago.
That could be an indicator that your TV doesn't support non-interlaced video modes via component. Some of these TVs can only do so, via composite.
The only way for that, is to use a modchip.