Small thing first, it is ASA rather than ACA (Agent Services Account), just so searches turn up the right HMRC pages.
Short answer is yes, both, and the order you set them up in matters.
The old HMRC Online Services for Agents account is still where PAYE, Self Assessment and Corporation Tax authorisations live. Those still run off agent codes and the 64-8 route, and you apply for a separate agent code for each of those services. So that account has to exist regardless.
The Agent Services Account is the newer one and it is where anything MTD sits, so MTD VAT and MTD for Income Tax, plus a few extras like the Trust Registration Service and the 60 day CGT on UK property service. One ASA per practice, you cannot run several.
The reason order matters: when you set up the ASA there is a step where you link your existing agent Government Gateway account to it. That link is what carries your existing client authorisations across. If you skip it, or you create the ASA against a brand new gateway ID before you have your agent codes, you can end up re-authorising clients from scratch. So get the old account and the agent codes in place first, then create the ASA and link.
One last thing that trips up new practices more than anything else on this list: HMRC will not issue agent codes until you are covered for anti money laundering supervision, either through your professional body or directly with HMRC AMLS if you are not a member of one. The HMRC route is not quick. If that is not already sorted it is worth starting now rather than after the code applications get knocked back.
