Being a Lead BA and a PM is definitely a challenge. It means that you're in a stretch role that has two different focuses, and sometimes conflicting objectives. Also, you'll find your working hours extending way into evenings and weekends to the stress of you and your team. I've had to play this dual role several times and what I've found to be important is delegating more of the BA work while empowering the BAs, having a mentor for the Project Management role if new to the role, and making sure to switch contexts often. These are described in greater detail below.
Lead BA Role - Delegate: Essentially, you want to take a much higher level view of the overall BA activities and manage those activities rather than participate in them. For example, if the typical BA activities consist of holding meetings, analyzing what you've heard, creating requirements, and estimating, have the other BAs own all of these activities. Make it your job to make sure that they are doing it in a timely manner. Be present/facilitate the more important "summary" meetings, but let your other BAs run the other meetings, and if possible, don't attend. If you have several BAs, and work that can be broken up into different components, divide the ownership of those components, but also make sure that each of the BAs are fully knowledgeable of the others' components so that you have coverage for absences, and inconsistencies and integration errors are reduced. In the meantime, make it your job to prioritize your BAs work, ensure communication between all the members is flowing, unblock any obstacles, and own the high level communication with your business stakeholders. At this point, you should be doing very little detailed analysis, at least for most of the components you're analyzing. Basically, you should be getting the Cliff Notes version of the analysis the team is doing.
This is a great opportunity for you to empower the other BAs, and get out of their way so that they can shine. If you have trouble with this, let me know and I can give you some more pointers.
Project Management Role - Find a Mentor: Hopefully your Team Leader will be able to mentor and assist you in the PM role. Regardless of who it is, you'll want to set up frequent meetings with this person to talk about the progress of the project. The first thing to do here with the help of your mentor is identify what your responsibilities are. Then find out what the true priorities are behind them, and if any of them are too difficult for you to manage into your schedule, see if you can alter it to make it more manageable. Be cognizant that, in this role, you likely won't have anyone reminding you that a deadline is coming up or that something is expected of you. The thing you don't want to do is walk in already having too much on your plate because plenty of time-intensive issues will arise and you'll soon find yourself dropping the ball. As the PM, you can really damage the relationship with the client if you drop the ball without communicating that the ball is going to drop in advance.
Context Switching: As the PM, you have to set the direction of the project, and constantly steer it to make sure it reaches its destination in the long term. As the BA Lead, you have a different schedule to manage with much shorter milestones that fits into the project timeline you set as the PM. You have to be able to jump back and forth between these two views of the project and see how both are progressing. Also, if you are managing other people in the PM role, you'll have to begin understanding their timelines and needs, and make sure to deal with any obstacles that come up for them. Even if you aren't managing other people, per se, you should hook up with other team leads and managers on or interacting with your project for frequent updates.
Let me know if this helps.
-Chereesca