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@osc 74HC595 is walkaround when you don't have enough pins but wiring and coding will be pain as I'm not sure neopixel library supports it.
For 5 strips you need 5 digital pins. I don't have M5Stack by hand right now but I'm pretty sure it can provide those.
My advice: Don't rush with 5 strips, do some examples with single strip or even 10-20 LEDS. No offence but I see you're not very common with electronics, may get stuck with 5 strips same time.
Some advices:
Yes, you can connect 5 strips into one huge strip but this will cause voltage drops most likely which leads to different powering experiments. Start with small amount of leds and code, than grow to full strip and when it satisfies you go to 5 strips.
Read about Interface, protocol, physical and software layers. This will help you to understand why i2c hub wont help.
Use legit power supply, M5Stack pin can hold up to 5 ws2182 leds guranteed. I don't remember how much ESP32 port provide, but I believe its something around 250 mA. Connecting heavy load on those may damage your M5 device.
When using separate power supply, make sure ground wires (black ones) are all connected (M5-strip-PSU)
Don't froget that U=IR (voltage = current*resistance). You can use this formula to calculate desired current or resistance aswell
