As many or as few as you like.
Just make sure you have two witnesses who are over 18.
Beyond that, it is entirely up to you, and your venue (and maybe budget) but let me know the numbers so that I can adjust the ceremony accordingly.
If you have only the 2 witnesses in attendance, the ceremony may be under 20 minutes but if you have 200 guests or more, you will want the ceremony to last longer than the time it took to seat everyone, and so you may wish extra readings or rituals to engage everyone in the process or at the very least, make sure everyone can see and hear what is happening.
Most have about the same number at their ceremony as at their reception but some have a large attendance at their Ceremony but a private reception while some have a private ceremony and huge Celebration.
Ask yourself, what you will enjoy most and then check your budget.
There may be little or no difference in the cost of your Celebrant, but the trimming will have a cost.
You have chosen to announce you love for each other to the world, so be confident in how you will do that.
