Dimensioning lumber by hand can seem like a lot of work and difficult to get right. You are right about the hard work part but it is fun work that will make you smile when it is done. As to the difficult part that is just a myth. It is very simple if you know the steps. I have a video On dimensioning smaller lumber by hand here: https://www.youtube.com/watch?v=ioOOWGqe_LA
Tools needed. #4 Hand plane setup for smoothing: http://amzn.to/2hc6LQZ
#5 Hand plane setup for a thick cut: http://amzn.to/2hUQtez
Scrub or foreplane: http://amzn.to/2hUQtez
#7 Joiner plane: http://amzn.to/2hUQtez
2 marking gauges: http://amzn.to/2hUQtez
Winding sticks: Shop made
Step 1: Learn About the Board
First, learn about the face using a pair of winding sticks and a straight edge of a plane. The winding sticks will tell you if there is any twist to the board and where it is. The straight edge will tell you if there is any cup or bow in the board. You may want to mark the high spots with a pencil or just keep them in mind. Now clamp it in the vice for planeing.
Step 2: Flatten Side One
Step 3: Flatten Edge One
Now that you have one reference side you just need the first edge to be 90degrees to the first side and flat. I start with the #5 and remove roughness from the mill. Once that is done I check all along the edge with a square to see where it is out of square and needs work. I use the #7 again to make sure it is in perfect flatness and also focusing on where it needs to be brought into square.
Step 4: Make It 90 Degrees
Once it is square all along the length and flat I might take one pass with the smoothing plane if it needs it. Before proceeding, I mark that side and edge. Now that we know they are correct I use those for reference surfaces throughout the whole joinery set.
Step 5: Flatten Edge Two
With the marking set to your width, Mark out the width of the board on both sides making sure to reference the first edge with the fence. If the scrap to be taken off is more than ¼” I use a saw to get close to the marking gauge line. But in this case, it is about ⅛” away, so I will jump straight to the planes. This step will feel very similar but I will be doing more work with the first plane to take off material. Also, I will not use the square as much as the marking gauge lines are what I am focusing for. Once I get close with the #5 hand plane then I switch to the #7 joiner and take it down to the marking gauge line. Last I will take one or two passes with the smoothing plane. If you want you can check it with the square but if the marking gauge lines were correct and you stopped at those points then it will be square.
Step 6: Flatten the Last Side
This is the side that normally takes the most work. Especially if there is a lot to remove. Start by using the marking gauge to mark out the thickness on both sides and both ends. Next, grab a scrub plane with an extremely heavy cut and start removing material. It is easiest to traverse the wood (go across the grain rather than with it) this may take some time depending on how much you have to remove. Always keep an eye on the marking gauge line all the way around the board to make sure you do not hit it with the scrub plane.
Step 7: Make It Smooth
Once you are close to the marking gauge line all the way around, switch over to the heavy set #5 and flatten out all the marks made with the scrub plane. This should bring things very close to the marking gauge line. You can use the straight edge of the plane to make sure there is not a belly in the center of the board. Next, grab the #7 and flatten the board and bring it all the way down to the marking gauge line. You may want to use the winding sticks, but if the lines were made correctly then it should be all good to go and parallel to the other side. Last smooth the surface with a smoothing land and you are done.