The way I think about it is this...
Question 1. Am I generating sufficient return on my assets to fund my FIRE budget and not deplete my capital base?
You have $2.6m in assets generating a return (ignoring, at this stage, that some can't be accessed for another 9 to 12 years). That might be 3 to 4% income and some growth that will hopefully negate inflation and not deplete your capital base in the long run. In the short term the growth will fluctuate.
3% income throws off $78k per annum. Franking credits bump that up a bit further, so you could probably achieve $70k after tax right now if you had no other income.
So based on your proposed FIRE budget and your asset position, you have enough in investible assets to FIRE. The problem is, between now and when you turn 60, only SOME of the assets and their returns are accessible.
Question 2. Do I have enough assets accessible to fund my Early Retirement?
So the next part is whether you have enough in assets outside of super to bridge the gap to when you can access super?
If all of your $2.6m was in super, you couldn't FIRE. Even though your assets were generating enough income to meet your needs, you couldn't access it for another 9 to 12 years.
If all of your $2.6m was outside of super, you COULD FIRE, since you know you're generating enough income and it would all be accessible.
In an ideal world, once you hit your preservation age you would ideally want all of your assets in super, since you can then put $1.7m into a pension account and everything* that flows from it is tax free. So you have up to $3.4m to play with between the two of you. If it's outside of super, you pay tax on it as you do now.
Your $1.4m currently invested outside of super might be delivering somewhere close to $42k in income, plus some franking credits. You could sell down a little bit to cover the gap to your $70k budget. The other $36k in income will be generated in super and reinvested. That should be more than enough to 'offset' what you have to sell down (bearing in mind you may have to pay a little bit of CGT). You have enough in total assets that you are no longer requiring that reinvested income in super to grow your asset base to an appropriate level for your retirement - it's already at that level.
More importantly, your $1.4m may need to be partially sold down, but you won't exhaust it over a 12 year time horizon at that level of spending.
Question 3. How do I best set myself up for retirement?
So you now know you have enough in total to FIRE. You also have enough outside of super to cover you to preservation age and the tax rules are better for assets in a pension account than outside super. So ideally, you want to be transitioning assets to super over the next 12 years. You have some caps on how much you can shovel in to super each year. And one thing to bear in mind is that once it's in there, it's there until preservation age - but that restriction gets less and less important the closer you get to that age. So if there's big purchases you may make in the interim, make sure you keep enough outside super to do so.
Based on your initial info, you already have enough outside of super for your lifestyle until 60, so you may want to think about shovelling as much as you can into super from now on, subject to contribution caps.
House or apartment?
The above assumes you stay in your current home, and you don't retain your current home, take the loan and downsize to an apartment. It also assumes that you FIRE immediately, which also doesn't sound realistic (which is a good thing from an asset perspective - you should be able to start loading into your super faster without selling down any assets at all). You'd need to relook at everything in that scenario. One thing you should be careful of is how you structure your loan and whether you'd get deductibility on the interest.
Based on my own experience, I'm not sure I completely agree with the idea that if you take the loan, you'll relinquish the option to drop out of the workforce. Your net asset position won't change that much under this scenario. You'll just have more (and different) assets and more debt. And a debt you could clear at any time by liquidating assets. Mrs G and I have actually just done something similar, although we're renting out the apartment and staying in the house in the short-term. If you'd like, feel free to DM me. I'd be happy to share a few more details there.
* Not quite everything.