Advice on Nintendo Switch setup, config etc.

ChilliBob

Hey everyone, 
My six and a half year old will be the lucky owner of an OLED switch come Christmas day!.. I personally haven't done or used any games consols for a long time - think psp, nds, a lot of ps2 and a tiny slice of PS3...

I have:
OLED consol
128gb switch specific memory card
Glass protector
Case
Mario kart, 
Mario Dulux thingy
3 months Nintendo online which came with it
Steering wheels
Switch Sports

Also from somebody else, ring fit thingy. 

I think I'm covered from the hardware and games perspective, (obviously the games library will expand).

So now I'm turning myself to Christmas day, these new consols aren't exactly a Mega Drive, as in plug them in, boom, you're playing Sonic in 5 minutes!

So, what can I do ahead of time to shortcut this for my son (and me lol)?

It looks like I need to create an account for myself, then hook his account as a child account off the back of this? Is that correct?

Also, I don't want him to be able to spend any 'real' money on this system without it triggering some approval from me - think Admin rights in a Windows domain type vibe. How can I sort this out?

Lastly, if I feel like some nostalgia and want to try nds games, or similar, am I right to think I'd need some enhanced version of Nintendo online?

Cheers all - feel like I'm embarking in a new world for both me and my son. I just want to make sure it slick, fun, safe and doesn't rinse me any more than it has!