You need to determine what you want the top elevation of your slab to be and then work down 4" from there in terms of where you want the top of your dirt to be. You will want to make sure it slopes away from the house for drainage, but it doesnt need to be severe.
Make sure and compact the dirt, the hand compactor you have is good. You dont want any grass, etc in that material, which i think you have removed.
You can just use cedar fence pickets for your expansion joint. However, you dont need an expansion joint in the middle of your slab, unless you just want one. For a construction joint, if you need one due to your placement capacity, etc then use a form until it the concrete hardens, and then pull that form and pour right up against it the next day (or few days) using the hardened concrete as your next form. If you want to reduce steel, then you will want rebar going across that joint. Rebar is deformed and is used to hold concrete together after it cracks or across joints. You would want that "tie bar" to be #3 bar 30" long spaced at 15 - 18" apart placed across the joint. Or if you run steel in the slab ( #3 bar 18" on center), you can have the steel go across that joint, but obviously that can be a challenge with forming. An expansion joint isn't needed, you donr have enough concrete to have an "expansion issue". Adjacent to your house slab we are "isolating" the house concrete from the patio to prevent one cracking the other as they will move different from each other due to the environment.
Best advice is to get a few bags of concrete and build some 1.5' x 1.5' steps to learn how to finish concrete before hand. Its harder than you think it is. Practice getting the right finish (broom, carpet, etc). You dont want to "over finish" it either. Get it flat with a 2 x 4, get it relatively finished, wait for bleed water to finish, then trowel it and broom it. After a few hours, keep it damp with water to cure it for a few days.
Don't forget that time, temperature, and wind impact concrete behavior. It has an expiration on it, you dont have a ton of time to mess around with it.
For concrete, look up volumetric trucks, I think concrete on demand might be a company you could use. They make the concrete right there on the spot for you. or Houston Shell and Concrete is a traditional ready mix truck as they tailor to small projects. If you go that route, order a bit more than you calculate you will need. You dont want to be short here. This is where a volumetric truck is nice.
You will want to ask for 3000 psi concrete with a target slump of 5". If they offer to use a admix******er or water reducer, those arent bad but may add some cost. They arent critical, but dont hurt. The admix******er will slow the set down giving you a but more working time and the water reducer will allow more workability with less water which will reduce bleed water. As the heat picks up, those become more important.
