@sittingonacornflake
You should be fine with the Lego you've got, even as a Lego novice, so no need to practise first.
The instructions are completely pictorial (apart from the occasional number if you need more than 1 of a brick), each page has a step of the construction to build - a box at the top shows which bricks you need for that step, so you can sort them out before you add them - then the picture shows where those bricks go.
Each step of construction generally uses 3-6 bricks. Occasionally it may have a picture to construct those bricks before adding it to the model - all very clear and straightforward.
Your almost 4 year old will need help, but my nephews at that age were finding bricks and doing parts of it alone, it's making sure the model is kept in the same direction of the picture and that the bricks are added the correct way that's really tricky at that age. They pick it up fast though generally.
Yes, I'm a massive Lego geek (in case it wasn't obvious)! 