Well....how many acres you have depends on a lot of things.
Wooded area is great if you want goats cause they love to browse in some wooded area so if you fenced in some of the woods with pasture in the front then that would be perfect for the goats. You could put the housing in the pasture area and then they would have access to grass and woody areas for browse as well. Depending on how many and what breed you want then that will determine the number of acres you want for them.
Do you want fruit/nut trees or space for berries and other fruits? If so then figure out how many, what type and where you would want to plant them. You can do it several ways...if you have a large open space to start with then you could plant the border of your "yard" with fruit trees and then possibly get bee hives later for pollenation. If you want grapevines or a blackberry/raspberry/blueberry patch then plan for your needs as well.
What do you want to grow for food? Lots of vegetables can be planted up near the house in borders for landscaping. Greens are especially pretty and need some shade so would do well near a house. Factor in larger scale crops in that as well. Like corn or grain crops. Do you want to use raised beds or traditionally tilled garden space? What kind of water are you gonna have? If you have well water then you are gonna have to think about how you are going to water the garden areas and the livestock and plan accordingly. I personally recommend water and electricity to the barns, especially for winter. Hauling buckets in the snow is NOT fun.
If you are starting from scratch you need to sit down and draw up a plan. At least then you can figure out what you want it to look like and when you look for land then you can work around what your plan looks like.
Another consideration is wooded area. If it were me, I would look for a mixture of open land and hardwoods. I also would look at buying a big enough piece of land that if need be, you could split off a couple of acres if you needed money. If you buy 25 and then later down the road need to split off 2-5 on the far side then that is a way to make some extra money in a pinch and still give you plenty of room. Another option with wooded area is the ability to hunt on your own land for deer/squirrel/rabbit/turkey. You could also selectively cut some mature hardwoods later on for extra money as well.
We live on 3 acres...not by choice. We were given this land but we offered to buy at least 8 more from our FIL and he refused and gave it to my BIL instead. Not fair but it's what we've got. The good news is that we can hunt on all the family land so we have access to almost 100 acres and 2 ponds to fish in. I wish we could have gotten much more open land cause we would have increased our livestock to include a few cows for meat/milk. For now we have a raised bed garden, small traditional plot of tilled soil, 6 blueberry bushes, 6 blackberry bushes, 2 beehives, 3 apple trees, 2 pear trees, 3 cherry trees, 80x110ft or so chicken run with 5 chickens and 4 indian runner ducks, 6 meat rabbits with their litters, 3 nigerian dwarf goats with a small barn divided up into 3 sections for hay storage/milk room and feed storage/goat area, we also have about 1/3-1/2 acre of open pasture fenced in for the goats next to the barn, 1500 sq ft house, 2 car garage/storage/shop area, and 3 almond trees. We also have a decent sized back yard for the kids to play in with a fire pit, playground area, and room for 2 tree swings and a trampoline. We also use a strip of land on the outer edge of our property on the other side of the fruit trees that we planted for a border to run meat chickens in a tractor every year. We produce a lot of our own food, especially meat. Last year was a disaster with the garden so hopefully we will have a better year now that we have been able to amend the soil with compost and poo.
I would like to add a greenhouse space either on the south facing side of the barn or the garage. We would also like to add a woodstove or solar eventually and get rid of the propane fireplace that we currently have.
Now, for our family of 4 that is plenty of space. Depending on your needs/wants go with more. I would not go with less than 3 acres and if the price is right and you have the money buy more. You can always sell off extra land but you can't always buy more if you need it later on. The other thing with buying more is the ability to split off a piece to give to one of your children later on. Not all children will want to do that but if you have more then the option is always there.
When mapping out a plan remember to include traffic lanes just like you would lay out furniture in a house. You don't want to put up a fence that you will have to cross over to get to something on the other side....we did and it sucks. I have to haul buckets of water to the meat chickens all the way around the goat fence and down the other side. We could move the chicken tractor but it would have relocate to the front yard and hubby doesn't want that. We are also planning on combining a new chicken coop inside the run with a lean-to space to shelter new double decker rabbit hutches. Leave yourself some open areas that could be used to add new things. We kind of got thrown into meat rabbits so now we have to rethink our arrangement. By building a bigger coop to house the ducks and chickens together (we currently have 2 smaller structures) we will be able to add a lean-to and put in a more efficient meat rabbit set up. Also think about sun exposure and wind when setting up areas too.