1. The nondeductible traditional IRA contribution that goes on 2019 Form 8606 line 1 is just the $2,455.88 (rounded to $2,456) of Roth IRA contribution recharacterized (not the $2,624.33 gain-adjusted amount transferred). This amount will fall through the calculations on the subsequent lines and appear as $2,455.88 on line 14 (assuming that you made to traditional IRA distributions or Roth conversions in 2019).
2. Line 14 of your 2019 Form 8606 carries forward to line 2 of your 2020 Form 8606. In TurboTax, click the Continue button on the page the lists the 1099-Rs that you've entered, indicate that you made nondeductible traditional IRA contributions and enter the $2,456 on the page that asks for you basis in nondeductible traditional IRA contributions. TurboTax will then include this on line 2.
You mentioned no other traditional IRA contributions for 2019, only Roth IRA contributions, so line 1 of the 2019 Form 8606 will show only $2,456 and line 2 of your 2020 Form 8606 will show only $2,456. If you made any nondeductible traditional IRA contributions for 2020, those will appear on line 1 of your 2020 Form 8606, including those nondeductible traditional IRA contributions that resulted from recharacterizations of Roth IRA contributions made for 2020.
3. Without knowing the details of your contributions made for 2020, it's impossible to say how much of you basis in nondeductible traditional IRA contributions applies to your 2020 Roth conversions and how much carries forward to 2021.
