The short answer is that you could run everything under a single LLC. However, having said that, you would want to keep a separate bank account for each entity to help facilitate tracking revenue and associated costs with each line of business.
You are going to want to track the profitability of each in order to help your decision making process when it comes to each business. If all of the costs and expenses are "thrown" into one bucket, it makes this type of analysis more difficult. Where possible if there are certain costs that are common to each, e.g., office supplies, etc., try to allocate among the three as best you can.
I'm new here and have a question on this same topic...My husband and I are starting three separate businesses but want to put them under 1 LLC.
One will be dba crafts
One will be dba transcription (which I've been doing for years)
One will be dba handyman services.
Under xyz LLC
How would I do the books for these businesses? I know I eventually need an accountant but I'd like to set up the books now and work with an accountant when the money is not so tight. Do I keep all the money separate for the three businesses or run it all through the LLC? Thanks.