I believe that they decided Savitar was going to be Barry at the beginning of the season, I honestly do. The evidence for this is that it's literally an idea they were going to do for season 2 with Zoom but decided instead to use Jay Garrick (Teddy Sears claims he was cast with this specific information in mind, so, no, they apparently didn't decided to make Garrick into Zoom halfway through, either).
Savitar's early appearance and early behavior probably stems from the fact that they wanted to try and differentiate this speedster from all the other ones. Any discrepancies between the early episodes' CGI model and the suit are just that: discrepancies.
The more I think about it, the more I think they should have gone with their original plan of making Zoom the evil Barry. I think they could have played almost all the same cards during that season and the reveal would have worked so much better.