Online shop and quit my job?

Most people start up while also keeping their current job. As orders flood in they can decide how to go. If no orders then they still have the day job to fall back on.

Er,good luck then

The internet is saturated with online 'businesses' and with a COL going on you will find it tough

How much salary do you need to be able to pay yourself in order to cover whatever living costs you have PLUS how much pension contribution do you need to make?

Why do you want to run an online shop? Do you have a specific product or niche that you think you have an advantage in?

Or are you just fed up of teaching and think this will be an easier, lower stress way of earning the same money that will also be done at home and fit easily around childcare/kids at school etc? If it is that, then it is a bit of a fantasy. You would likely be better off trying to find a salaried role in a different job.

I think it's harder to make money doing this than it used to be a couple of years ago. Sites like Etsy have been flooded by cheap mass produced tat which makes it harder for individuals selling bespoke products.

This.

Running a business is so much more than just setting up a shop and expecting people to buy.

Its a hard long graft and much much harder than I expected it to be (although I am in a slightly different sector).

So I would say, give it a go but don't give up your day job yet.

Sounds a bit vague to me. You need to work it out from a business perspective - what would the running costs be compared to the income you generated? How would you market your product etc etc.
Id start the shop and run it alongside my teaching for a while, then drop the secure job only if and when the shop takes off.

As already asked what is the line of business that you want to go into?

When you say you don't know where to start do you mean as in you don't know what you'd like to do
Or
You don't know how to put the business out there?

Edited to say...no you're not being a dick for wanting to give it a try.

What are wanting to sell? Are you thinking using an established online store (eg Etsy) or setting up your own website? Have you done a basic business plan to work out costs, taxes, etc? What's your marketing plan?

What is unique about your product that will make people buy from you and not elsewhere and how will they find out about your online shop?

How much start up capital do you have?
What sort of items will you sell?
How and where will you advertise to get your site known?
Are you able to deal with the web design, etc yourself?
Who is your target audience?

Have you sold your products consistently to know there’s a market for them? Also be aware of the high fees from the likes of Etsy

You've no idea where to start so in the kindest possible way, I'd say this is a poor idea. If you're looking to change direction job-wise then it needs to be with some knowledge and understanding of what you plan to do