Yes. There are just two considerations.
First, check the Rules of Procedure – being on some Committees officially rules you out of joining certain others. There aren’t many conflicts like this, but it’s worth being sure before you start making plans.
Second, think about how much work you’re taking on. Most Committees will meet at least once a fortnight, and meetings can be half a day long – maybe even more. You will get papers a few days in advance, and you’ll probably need at least a day to read through them. If there’s something on the agenda that interests or concerns you, you may want to set aside additional time to research it.
In addition to that, you have three-day States Meetings every month, and a considerable amount of preparation for those. And you have constituency work, and an absurd amount of emails to deal with.
Two Committees is probably the optimal number. I sat on four Committees for most of last term: two big (HSC and ESS) and two comparatively small (OADC and SACC). Let me tell you, that was silly. It was only possible because I had no other work responsibilities and (for most of the term) little in the way of family responsibilities. I don’t recommend it. Two Committees of any size, or a Presidency of one Committee and a minor role on another, is a far more sensible approach!
In the end, you’re the judge of your own workload, and you know what you want to focus on in the States. Let that guide you in terms of which Committees you join, and how many. But do be careful not to overload yourself – you need to allow yourself enough hours in the day that you can do justice to the work you’ve signed up for.