Still gathering requirements...
A) assuming this was your only income, you would be taxed as if this was salary..same as normal PAYE (but without the NI).. use a tax calculator (like listentotaxman et al) to get an estimate.
B) no - once you've settled all tax owed on the loan you are exempt from the 2019 charge.
The purpose of the 2019 loan charge is to draw a line under loan schemes without the government having to resort to lengthy court cases and (in their view) delaying tactics. It works by treating all outstanding prescribed Trust loans (i.e. loans from identified scheme trusts) as at April 2019 as income in the 2019-2020 tax year (i.e. if you have £100k of loans for all years, your income for 2019-20 would be increased by that £100k and then taxed at standard rates - so, roughly speaking, if your normal income for that year was £50k, your adjusted taxable income for the year would be set at £150k - meaning all of the loans will be taxed at the higher income rates, whereas atleast some would have been lower rate taxed if you settled each year separately). If you have settled the taxed owed before April 2019 you are exempt.