To explain retirement accounts better, you have to look at each account as a BUCKET of funds. Each BUCKET has its purpose and reason for existing.
IRA: (Max $5,500/yr.) BUCKET started by yourself used to avoid taxes on principal and gains until retirement time. You CANNOT touch the principal OR the gains until retirement date set by government.
(OR)
ROTH IRA: (Max $5,500/yr.) BUCKET started by yourself used to avoid paying taxes on gains. Taxes on principal are paid that tax year. Good for stuffing more value into your IRA accounts than a regular IRA considering you haven't paid taxes yet on the $5,500 in the regular IRA, but the amount is still the same. (This is only the case if you max it out. If you do not max it, you may get better value out of the regular IRA) You can also touch the PRINCIPAL (not the gains) at any time should an emergency come up.
401k: (Max $17,500/yr. or plan Maximum) BUCKET started by your employer used to avoid paying taxes on principal and gains. You CANNOT touch the principal OR the gains until retirement date set by government.
(OR)
ROTH 401k: (Max $17,500 or plan Maximum) BUCKET started by your employer used to avoid paying taxes on gains. Taxes on principal are paid that tax year. Good for stuffing more value into your 401k accounts than a regular 401k considering you haven't paid taxes yet on the $17,500 in the regular 401k, but the amount is still the same.
Taxable Account: (No Max) BUCKET started by you to invest with. You can do whatever you want with the money at any time with no penalties, gains included. Taxes are paid on principal and gains each year.
As for your questions about taking the principal out of vanguard, I would assume at most a week or two? I've never done it myself, but I don't see why it would take longer than that. Again, this is emergency use only. I'm sure you could use a credit card for the emergency (whatever it is) and pay it off when you receive the funds a week or two later.
As for the ROTH, forgive me, it's ALL of the principal and up to 10 percent of the gains (without paying taxes) provided it has been at least five years. With the regular IRA, it's a max of $10,000. More info here:
http://www.wikihow.com/Buy-a-Home-With-IRA-MoneyEDIT: Each BUCKET mentioned above holds the money with which you purchase index funds, stocks, bonds, etc. Those index funds, stocks, bonds, etc. sit inside that bucket alongside your money.