Does it matter what number goes into the value?
Yes. The more points a question is worth, the more impact it will have on the final score. (E.g. a 10 point question in a 50% group will have more impact than if the same question had a 1 point value in a 50% group.)
Is there anyway to get an even flat percentage score rather than a decimal?
You mean having the UI say "100%" or "74%" instead of "100.00%" or "74.25%?" No. It always shows two decimal places.
When calculating the question group is it possible for it to calculate based on the weight score and not as a whole 100%?
If I understand the question, no. In Preview mode, PureCloud calculates the score based on the questions you have answered so far. It has no information either way (should it assign the points or not?) about the other questions, so it doesn't include them in the calculation in until you answer the question.
However, only you as the form designer will ever see that behavior. When evaluators are completing an evaluation, they don't see a score preview as they answer questions. PureCloud also won't let them submit an evaluation unless they've answered all questions (unless you marked some as N/A when designing the form), so PureCloud will always have information from every applicable question when it calculates the score for an agent.