You are young - so your spending now is unlikely to be the same when you reach your financial goals and retire. That said - they may be similar if you retire young, when you have kids.
Maxing out the 401k is important. You mention your employer's contribution as part of the 18k limit... I don't think that's how it works... I maxed out MY contributions to the max - and my employer's contribution was on top of that.
I hear you on the childcare and 529's. My kids are now 14 and 16 - so no daycare... (which was obscenely expensive)... but even without that they add costs to our budget. And even though retired, we're still trickling more money into their 529's each month. The 16 year old is wanting to learn to drive... that will get pricey quick - insurance, gas, a vehicle...
There are two ways to approach what your spending will be in retirement - (and it won't be 80%).
Top down - take your gross pay, subtract out things that won't be there in retirement, and add in things that increase in retirement. So you subtract out FICA taxes, 401k contributions, savings contributions, and work related costs... You add in healthcare increases, and if you plan to travel - you'll probably need to add that in.
Bottom up is where you take all of your annual spending by category (including taxes, healthcare, etc)
When your top down and bottom up numbers are close -then you probably have a good idea of what your real expected spending will be.