What are the advantages to having your own family milk cow?
Here is our situation and why I ask. I had a 2 month old Jersey calf for about two months. I got her on a trade for some goats and I really wanted to keep her but needed money to purchase my LGDs and had decided she was just too young to have to feed for two years before getting any "return" from her. Anyhow with our smaller acreage what I REALLY wanted was a Dexter.
So now I have come across the "perfect" cow. A Dexter 2 years old and due this month. The breeder said he would hold her until after she calves so I don't have to deal with that (I hate to move her anyway so close to birthing). She is super friendly (was a bottle calf) only about 550# and pretty black!! So for $850 I would get a lactating young cow with her calf at her side.
My DH is saying 850 will buy a LOT of milk!! True, but what's in that milk I"m buying - right? Since we raise goats, chickens and pigs I do know that raising your own meat isn't always cheaper than going to the store to buy it.
So can anybody help me out and give me reasons to forward to my DH as to why this can be a good investment? Can anybody give me reasons why this WOULDN'T be a good investment? Of course I might not forward those replies to the DH

but it could help me in the long run.
Here's some things I thought of:
You get alot more than "just milk" from a milk cow, you get cheese, icecream and butter (of which we go thru a lot of those things as well).
I could sell her calf if it's a heifer and recoup some money within a few months.
I could keep a bull calf for meat (prefer to put at least 1/2 in our freezer and sell the rest)
And of course in the future the above two things hold true for every calf she has.
If all else fails I could most likely get my money back out of her (unlike horses nowdays cows seem to hold their value).
Oh and if we do have any "extra" milk I have chickens and pigs that would just LOVE to grow big and strong on it.
Can I slaughter a Dexter steer at around 12 months and still get a decent return or am I better off waiting until a bit older?