Is hydroquinone or similar lightening agent necessary after first Halo facial?

Great question! It's hard to give you the best answer without seeing you in person. I've personally found that olive / mediterranean or darker skin has a better result and less risk of hyperpigmentation after lasers if treated with hydroquinone. Research actually shows that starting as early as 3 days after treatment - even before you peel is both safe and gives the best results. For more Irish (strawberry blonde, very pale / pinkish skin tone) this is less important, but still may give a bit better improvement in sun damage / freckles.

Yes if you scored iv and above as skin type you need to use it one week pre and 2 weeks post every time you get a halo done just to protect your from any potential burns/ hyper pigmentation. If you are skin type i - iii its not necessary. 

I think it's an excellent idea to continue using hydroquinone or a botanical skin brightener both before and after your procedures to get the best results. Alternating between the two every few months is ideal.  Using these in addition to a retinoid and daily sun protection is what we also recommend to maintain your excellent results. Staying on a regime like this with a combination of broadband light treatments and Halos will pay off not only in the short term, but in the long run for beautiful skin as you age.Goof Job!