If you do some research, you'll find there are
many, many custom layouts out there (Simplified Dvorak, Programmer's Dvorak, Colemak, Workman, Neo, AdNW, QGMLWB, etc, etc). I suggest you read up on people's experiences with using various layouts before deciding, too. For instance:
https://geekhack.org/index.php?topic=74943.0The problem with using a layout that has similarities to QWERTY and using the same physical layout is that you're essentially retraining your QWERTY muscle memory to the new layout which can really mess you up when switching between them (as many people will need to be able to do for various reasons, such as if you're visiting someone and need to use their PC, etc.).
Which is why I recommend going for a fully customised, fully optimised layout, tailored to your own preferences (alternation vs rolls, etc),
but only on a different physical layout board. The physical layout has more benefits in terms of efficiency, ergonomics, RSI, etc, than the character layout.
I recommend the AdNW software for analysing and customising your layouts as you can alter the weighting of different optimisation factors (key position distance factors, inward rolls, outward rolls, alternation, same finger, etc) and provide your own corpus for the analysis and optimisations.
Keeping ZXCV positions for common shortcuts is not a good thing to do, either. It retains too much similarity to QWERTY and can really mess with the optimisation of the layout. I have found it very easy to learn the same shortcuts on my own layout board as part of the training process.
That way, you keep your QWERTY typing skills in place while learning (and normal QWERTY typing is still very useful to be able to do for a lot of reasons) and don't suffer if you have to switch between them. Eventually you may lose a little proficiency with QWERTY due to not using it for long stretches if you're using your custom board most of the time, but it's not something that'll ever fade completely.
You can do some basic comparisons of different layouts here:
http://patorjk.com/keyboard-layout-analyzer/#/resultsYou can post your own text into the main field and run the test. There are LOTS of existing layouts for you to compare there (including QGMLWY, but you can easily modify an existing layout or make your own for testing, too) and the statistics after running the test can be quite revealing, particularly the finger / hand balance and heatmaps.