Question 1For a rough approximation, with a number of assumptions/simplifications that you can tweak:
Use this:
http://www.bankrate.com/calculators/savings/simple-savings-calculator.aspxStart with your $225k net worth (not including the value of your house), adding $4.5k monthly, w/ a return of (say) 5.5% (which you could say is an 8% return less a 2.5% inflation).
The results show $1.75MM after 15 years, when you're 45.
From that future nest egg, we often talk about a 4% year safe-withdrawal rate. That would be $70k, which goes well beyond your $45k expenses. But 4% is often considered to be safe for 30 years (IIRC), and you'd only be 75 years old at that point, so perhaps you want something safer than 4%.
A 3% SWR gives an annual spend of $52k.
If you want to get $45k after-tax, then $52k pre-tax is pretty near satisfying that number.
Feel free to play with the numbers to reflect either what you feel the future holds and/or how large of safety margins make you comfortable. We all do it. ;^)
Question 2Just an opinion, since I've not done it either ...
I'm not dialing back my 401k, nor do I think you should. If I did the math right, you're saving $17.5k in 401k, $11k in IRAs, and $25k in taxable yearly. So you're already pretty evenly split between sheltered/taxable savings. That's pretty good IMO. Over the next 15 years your income will grow. Since you've run out of tax-sheltered room, and since you're guarding against lifestyle inflation, you're going to end up putting that extra money into taxable accounts. So via a "natural" process you will begin to save more in taxable than you do in sheltered. I'd leave it at that and call it good.
FWIW, I do plan on doing the 72(t) in the future. So I suppose that may color my perspective.
(Does your company's 401k plan support non-sheltered after-tax contributions w/ roll-overs into a Roth 401k? Mine does, and I'm able to save an additional $20k/year into a Roth 401k that works basically like a Roth IRA. The ability to have future access to these contributions before retirement age is comforting. There are a number of threads on this approach, if you search.)