Hi Sai
Although both 3.5 flow and 7.3 flow sits in the same system, both uses different methodologies to transform the data which you are aware of.
Hence we do not have a specific method to compare both. But if you haven't got any error during migration, it shows that the migration went well and there is no issues.
In few cases, some complex routines might not be migrated properly and it will throw error during that phase. If you haven't got any error, I think the migration went well and its all good now
If you still have doubts, no need to check all the fields as you might have many. Just choose one per rule type. like choose one field which has field routine and compare. choose one field from formulae and compare.
If you have encountered any issues, please post here, we will analyse and help you to resolve it
Regards
Karthik