In the last 5-7 years, I've gradually invested money in several mutual funds via my bank (USAA). These funds now make up about a third of my portfolio. Initially I had invested in these funds because it was very easy to do: I already had an account at the bank, and the online system made it simple to create mutual fund accounts and set up auto-investing.
However, more recently I've started to take more notice of how high the expense ratios are on these funds. I'm considering opening up some accounts at Vanguard and moving my money there, into index funds that cover the same categories but with substantially lower expenses.
My existing funds (at least, the ones I'm planning on moving) are in taxable accounts. As I understand it, as long as I remain in the 15% tax bracket or lower (which is where I currently am), my long-term capital gains tax rate is zero, so I could sell these funds and use the money to buy into lower-expense Vanguard funds with effectively zero cost (as long as I don't sell enough to push me into a higher bracket in any single year). So that's what I'm contemplating: gradually selling off the USAA funds --- as much as I can each year without incurring taxes --- and instead buying cheaper Vanguard funds.
So my question is: is this a good plan? Am I understanding the tax situation correctly, such that I can really do this at no cost? Is it worth it to worry about the taxes, or should I just move all the money at once (even though it would definitely push me into a higher bracket and incur a tax)? Also, supposing I try to avoid the tax in the way I outlined, is there any way to do it other than keeping careful track of my expenses and, at the very end of the year, selling just as much as I think I can safely sell? (It's obviously not the end of the world if I accidentally sell $100 too much and have to pay a small tax, but, also obviously, I'd rather avoid it, and I'm curious if there's any way to do so that doesn't rely on my own accuracy in knowing exactly what my income was.)