Me too, Australian outback, not many people around here of any sort and not many who would know much about CAD.
It's a steep learning curve, but read the wiki and keep at it, it will get easier over time.
Your sketch is not valid, at least not for PartDesign WB or most others because it does not describe one single (or sets of single) contiguous faces.
Like Chris said, simplify the sketch. It's best to have more than one more simple sketch rather than one overly complex sketch in most cases.
For example in this case, spilt the sketches by using logic, perhaps the way you might make the object in the real world.
1) sketch the back plate with no details or at least only a few
2) Sketch the fan cut outs in another sketch
3) sketch the bolt holes and slots in the next sketch
Another tip, consider storing values in one convenient location, like a spreadsheet (or for more simple things perhaps just use it in a property where first used) then reference those values where needed with an Expression. FGor example, lets say the bolt holes are 6mm diameter, you can use that value in both the slots and round holes, if stored in a spreadsheet cell then it is easy to come back later and change the value to say 8mm and have the model automatically update everything.
As Chris said, rather than using distance or similar constraint on everything that is the same, just use "equals" constraint etc.
These screen shots are your sketch and the same one in edit mode
What are you wanting to do with these sketches? I assume that you are going to model the solid in PartDesign.
I will spend a few minutes making a demonstration based on your file...back in a bit
A quick side note of some nice news, all to little of that this year for most of us, over night Chloe had twins! Clover and Hazel, both girls and very cute, my girls have repeatedly been down the paddock cuddling them and giving Chloe food and water so she doesn't have to go far from them. They are so small when new born and their legs seem too long (out of proportion). For anyone less well informed, Chloe is my family's very, very, fat and much loved pet goat! If you are interested I could post a photo in our "Pets" topic?
OS: Ubuntu 18.04.5 LTS (KDE/plasma)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19. PPA
Build type: Release
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/Australia (en_AU)