OP - I'd advise you to discuss this fully with DH wrt all aspects of your routine. This will be a massivie change for you both, so you both need to be fully aware of exactly where you stand.
The 'going with the flow' attitude does not work and I have personal experience to back this up.
Your DH will go from FT work - chatting with colleagues, banter, out of the house, breaks, mental stimulation, to home all day with DS - yes he can go to the park, do the shopping, housework etc but although he doesn't realise this at the moment, it will be the adult company he eventually craves and could perhaps resent you for being the one with 'the life' outside of the home.
At the moment DH is perhaps thinking 'oh, I could do with some time off work' (we all do don't we?) but give it 3 months and then he may start to get bored.
That's why I suggest a full and frank discussion to set some rules :)
When you come home from work it's more stressful for you to be met with a more subdued DH, not only are you feeling guilty about leaving DS, you're also feeling guilty that DH is not the 'captain of industry' he once was.
IME, I reckon you will be ok with this and it will make your time with DS more special - the only thing that ever stresses me out is DP and how he feels on a daily basis.
My DP has been SAHD for our 10 month old ever since I went back to work 7 months ago - we thought we'd 'go with the flow' but encountered many problems and eventually had to set some rules. (and things are going great for us at the moment)
I could go on and on here, but perhaps you're already thinking shut up Velvet, you're banging on a bit here 
Just make sure you both discuss this and both agree and understand what will be expected of you, in terms of finances, housework, childcare, sleep & naptimes, free time, family time....the whole shabang!