Bob
700/7000 horsemen is viewed by nearly everyone as a copyist error, not a contradiction.
David's sin penalty of 7 years is also abundantly agreed on to be a copyist error because the rest of the 2 verses are in complete accordance with one another.
The hebrew word used in Exodus 9:6 is meant specifically for livestock and therefore does not include the horses used for the horsemen of the chariots. Therefore, not a contradiction because all the livestock were killed.
The plague referred to in 1 Corin. 10:8 is not the same plague as the one in Numbers 25:9. Paul quotes Exodus 32 just prior to giving the number as 23,000 which is a completely different plague than the one in Numbers 25:9 as punishment for those joined to Baal. Therefore, not a contradiction.