Can I use an Apple 70W USB-C Power Adapter with a 13-inch, 2018 MacBook Pro?

My understanding:

USB-C Power Delivery – the type that can provide large amounts of power – is negotiated. Both sides must agree on a voltage and a power delivery direction. The cable must contain chips to tell them that it is capable of carrying more than 15W of 5V power, or they will refuse to send large amount of power over it.

I believe that when your MBP came out, the standards allowed delivery of a maximum of 100W (20V, 5A). There is no harm in using a 240W cable, but it won't offer faster charging rates than a 100W cable, given that the MBP will never try to charge at >100W.

Yes you can.

To realize full performance you def want to use a USB-C cable which can charge at higher rates. (not all can)

The cable that came from Apple with your MBP — if you still have it — is by definition suitable.

your computer appears to have shipped with this power adapter:

13-inch MacBook Pro models introduced in 2016 or later

Apple 61W USB-C Power Adapter and USB-C Charge Cable

Use a power adapter with your Mac - Apple Support

You can always use a Power adapter LARGER than the original. Your Mac only draws what it wants and ignores the rest.

USB cables that provide charging come in three flavors:

default 60 Watts

premium 100 Watts

super-premium 240 Watts.

for best results, use one rated higher than the default.

Yes!

No harm, the macOS can negotiate the proper wattage without issue.