Were the Jerusalem believers in Acts still practicing Judaism and temple worship?
Yes. The believing Jews at Jerusalem formed a called-out assembly, yet they remained under the total umbrella of Judaism. They had not separated themselves from the Law or temple worship, but assembled as believing Jews while still participating in those Jewish practices.
Les explains that the believing Jews at Jerusalem were an Ecclesia, a called-out assembly. They were called out of Judaism and met apart, yet they remained under the total umbrella of Judaism. They had not separated themselves from the Law or from temple worship. They were assembling as believing Jews, so their faith in Jesus existed alongside ongoing Jewish religious practice and temple worship rather than in separation from it.