Welcome to the forum,
The long twist is easier to make in my opinion, in computer modeling the short twist shows a very slight gain advantage but only when the twist is done very accurately. It would be very hard to tell the performance difference between the 2 if at all so I think going with the easier, more forgiving long twist is the way to go for most.
Bigger is better only because the size matches the current grouping of channels here in the US ch 14 - 52 better. Any bigger than 10" whisker and 9 1/2" phase line will start to drop the gain curve of the antenna below that channel range and wouldn't be very good above ch 45 or so. It also works out that improved VHF-hi ch 7 - 13 works for the whisker/phase line sizes in the 9 - 10" range.
The large angled reflectors can generate more reflected signal but there is a point on diminishing returns that really starts to come into effect around 40" wide. Wider will still gain a little, maybe a db or less but the reflector curve has to be very accurate to take advantage of it.