Although there are only a few entries for week 3 handicap races I see there are a couple of mistakes already.
We have to keep it as simple and straightforward as possible, so here's my thoughts.

Instead of having (65-80) (81-95) (96-110) just have one race perhaps (0-110) and if there are more than say 20 runners then split the race into 2 races according to there handicap mark. If there were less than 20 runners then you could just leave it as one race, this should prevent races with very small fields.

In the event of a horse entered in a handicap race over a distance that it has not run before it should be allowed to race. When the race is run, a quick check to see that the winner is eligible can be done and if it is found that the winner is not eligible then it will be disqualified but keep the handicap mark it gained in the race. Whether the race should be re-run or places manually adjusted I have no strong opinion on (whatever is easier). This would mean you wouldn't have to check entries beforehand which would be time consuming.

I'm not asking for this to be set in stone, just some food for thought to keep things simple.