You can cut your cloth to measure once you’re above a certain investment level of about 6k or so, imo. This is because an inverter is more or less a fixed price so you won’t cover the cost of one with 3 panels. But once you’re up around 8 or more panels, you’re fine. Battery size is more dependent on your usage profile, but can be paid for by either supporting your own self-consumption or supporting a buy-low-sell-high export strategy, ie buy cheap overnight electricity to use during the day and get paid for most of your solar exporting to the grid.