I can't speak to actual numbers here, but without the RO membrane I think you'll find that you're going to expend your DI resin extremely fast to the point where it may not make economical sense for the amount of water you would produce.
You might want to consider a multi-stage particulate and carbon system to see what those results are if you don't want to go full RO/DI. At the same time, unless you're trying to do something specific with modifying your water, I think the parameters you posted above are decent for just keeping fish. Unless aiming for breeding (or keeping wilds) for example, I prefer the stable conditions of my water year round over trying to chase some number.