Hi
DS was already at nursery due to me working when I left a job and started to freelance (I do marketing). We were in the lucky position of just about being able to cover the fees on DHs money should I not earn anything. 
I was attracted to a nursery for all the reasons you gave. For me it provided minimum hassle and DS was v happy there. I might just have a robust child, but I think he only had a couple of days out of nursery over the 4 years he was there. I found nursery very parent focused and turning your child away was the last resort!
I think the main downside will be the lack of flexibility over days (should you need that) which you might be able to negotiate with a child-minder.
DS was in 4 days a week and I managed to not work on the Friday. I personally found I could meet client's needs during these days. Sometimes working of an evening if really busy etc.
As for which days, it depends on when your clients need you, but I would think about Tues/Wed and Thurs. If a client rings on a Mon, you then have 3 days to do the work that week? I have found Mons & Fris are generally when clients are focused on other things etc. It might also depend on what the nursery is willing to offer, some don't do Tues/Wed/Thurs combo, but as you have 4 to choose from they might be more accommodating/competative.
I know from this board (and as Talkin proves) there are lots of freelance MNtters who are able to manage without childcare but for me I needed that time to develop business & deliver work. I needed to know where I was as such.
I also think for me the reality of having to pay for childcare focused me on the business.
Not sure if this is any help. Good luck with it all.