What is the highest percentage of extras conceded in a Test?
And has anyone else done the double of 1000 runs and 100 wickets in a year as Kapil Dev has?

Pakistan's 52 extras made up 16.3% of Australia's total of 318, the sixth highest percentage of extras conceded • Associated Press
Australia's 318 in the exciting Test in Melbourne last week included 52 extras (20 byes, 15 leg-byes and wides, and two no-balls), which accounts for 16.3% of the total. This actually comes in sixth on the list of highest percentages of extras in a Test innings, looking at completed innings only.
You're right that ten of the Australian team which took on Pakistan in the first two Tests - in Perth and at the MCG - had amassed more than 1000 runs. The exception was Josh Hazlewood, who started the series with 465.
You're right that in Tests and one-day internationals in 1983 (no T20s back then), Kapil Dev scored 1106 runs and collected exactly 100 wickets. And it turns out that Kapil is unique - no one else has managed this excellent double.
This has not yet happened in a Test match, although there are two instances of someone scoring a triple-century and a single hundred in the same game - Graham Gooch hit 333 and 123 for England against India at Lord's in 1990, and Kumar Sangakkara followed suit with 319 and 105 for Sri Lanka against Bangladesh in Chattogram in 2014. There have been six other instances of a double-century and a hundred in the same Test.
Indian fans will be relieved to learn that this is not true. India have now played 18 Tests that started on December 26, and although their record in them is not great - the defeat in Centurion the other day was their 11th loss - they have won four: against South Africa in Durban in 2010 and in Centurion in 2021, and against Australia in Melbourne in 2018 and again in 2020. They have also drawn three.
Steven Lynch is the editor of the updated edition of Wisden on the Ashes