Retirement tax questions

There is a difference between contributing to a Roth IRA during a year and rolling over funds from one retirement plan into a Roth IRA during the year.

You can rollover as much as you want from another retirement plan (except a 409A Plan) to a Roth IRA during a tax year.  However, you will be taxed on the amount of pre-tax funds that are rolled over to the Roth IRA.  So if you had a pre-tax 401(k) plan that you want to roll over into a Roth IRA, then the entire amount you roll over will be taxed in the year you do the transfer.  If you were rolling over from a Traditional IRA to a Roth IRA, and all your contributions to the Traditional IRA were pre-tax contributions, then you will be taxed on the entire amount you roll over.  If, however, you have pre-tax and after-tax amounts in your IRA accounts (i.e. made contributions at some point of time to your Traditional IRA but did not deduct those contributions on your tax return), then the rollover from pre-tax to Roth IRA will be taxed pro-rata, based on the ratio of pre-tax to after-tax funds in all your Traditional IRA accounts.  But there is no limit on the dollar amount you can roll over. 

As to the question on differences between converting money from a Traditional or a Roth IRA - the differences would be on what amounts are being taxed.  A rollover from a Traditional to a Roth will have a taxable impact to the extent that there are pre-tsx dollars in your Traditional IRA account. A rollover from a Roth IRA to a Roth IRA will  have no taxable implications, as you are just moving funds from one after-tax account to another after-tax account.  If doing a Roth IRA to Roth IRA rollover, please be aware you can only do one rollover in any 12-month period.

As for your final question, doing a contribution is considered a separate transaction than doing a rollover.  Therefore, you can make contributions to your Roth IRA's up to the contribution limit regardless of doing a rollover into a Roth IRA account.