Let's assume I'm playing a DD with 2 other players. My system of choice is hi-opt1 (side count aces only). I'm on my 2nd round.

A habit I have in the earlier rounds is to make a mental note of how many (7s to 9s) are exposed. I don't side count these, but it doesn't require much brain power to take notice on round 2.

Roughly 19 cards are exposed (roughly 5/6 deck remaining)
1st round: 11.8 cards dealt (~2.7 * 4)
2nd round: 7 cards exposed

I have a bunch of hands in mind. I'll throw just one for now since there are a lot of questions I don't have a clue how to approach.

Hand 1: 12 v 4
RC: 3
TC: 2 1/2 (I'd probably truncate to 2 at game speed)

The index play is somewhere slightly above 0 if I recall correctly.

Q1: What are the effects of middle card? My hunch says
7s help the dealer a lot and helps the player,
8s harm the dealer and helps the player a lot,
9s harm the dealer and helps the player a lot.

Q2: What are the estimated EORs? How does that translate to adjusting index plays for surplus and shortages?

Q3: What should be done if no 7s, 8s, or 9s are dealt? According to one chart i found, a surplus of one 7 means TC should be reduced by 1. There is already a surplus of 1.5 (I'd probably truncate to 1 at game speed) 7s. Now how do I factor in the other surplus of 8s, and 9s?

Q4: If I also notice no 5s or 6s (a bunch of 3s and 4s instead) are dealt, how do I incorporate those into my beginning round strategy? I'm assuming they are just as helpful and should be adjusted into the play decision even though they already have a +1 index attached by default in hi-opt1.

Q5: What are some other key hands to pay attention to. 16 vs. 10 seems important since it's the most frequent. Hands involving 2s,3s,4s (splitting or not splitting in NDAS games perhaps) seems interesting too since I'd imagine EOR factors mattering a lot.

Thanks!