Realistically though, that would probably be something not contained in the constitution, right? Our current constitution is very vague with regards to how elections are run, if I remember correctly.
It's because our election system has been amended piecemeal to try and suit different demands and tastes over time. Whatever system that is chosen (open PR or party list PR) will to an extent depend on what people want; party based politics or personality based politics (or a mix). I am in favour of a PR system but whether it is a party list should really depend on the government system chosen. In some circumstances it can work very well, in others it may be seen as 'restrictive' if your favoured candidate has been shunted down the list because of party politics. It also cause some pissed off party members quitting and running as a one person list
Which could be a good or a bad thing!
On the issue of the president, in this I agree that he should have powers that act as a counterweight to the PM. I think that was touched upon here;
https://uselectionatlas.org/FORUM/index.php?topic=94209.msg1953553#msg1953553
