Fuses and breakers, we use 1.25x. Whatever maximum continuous load you expect (say 16A), make the breaker 1.25x (e.g. 20A). That avoids nuisance trips.
PV panels, whatever Isc they have, we apply an additional 1.25x because they can get extra illumination off clouds in addition to direct. 1.25 x 1.25 = 1.56, so if Isc = 10A, fuse should be at least 15.6A, make that 16A or larger.
You can over-panel most inverters and charge controllers. If you put 12 kW of PV panels on a 10kW inverter, it will put out at most 10 kW. The extra panels help make full power for more time, various seasons, slight overcast.
Note that micro inverters often feature how big a panel they can tolerate like up to 500W. But maybe they only produce 280W of AC regardless. That is OK, but you are missing out.
If your inverter can take two parallel panels or series strings of panels, those can be oriented toward morning and evening sun; lower peak power but more hours. If a 90 degree angle between them I estimate 0.7x the peak. So 15kW of panels as two, 7.5 kW arrays pointed different directions would never exceed capacity of a 10kW inverter, just give more hours production.
Battery inverters have to be able to start your loads. Estimate 5x nameplate rating. A 400W small window A/C needs 2000W to start, only for about one second. Inverter and battery has to deliver that.
Battery, some people size 3x daily consumption, to get by if cloudy. I sized for just one night; my system is only for occasional power failure.
Find out what model panel, what model micro inverter, and how many. You should know in advance how much power it will produce.
For grid tie, it is common to put in whatever will offset your annual usage, or just what fits easily. It might produce extra in the summer and you draw extra from grid in winter. To run off-grid, it has to meet your needs year-round.
