Garden Project needs Help

I need some help regarding my garden project I've taken on board which is huge specially my knowledge in the area is limited (none), only what information I can find online really. I've got list of endless questions at the moment and will be really thankful to all advices.
I've got a decent size back and side garden in triangle shape. It has been neglected by the previous owner to extreme and had got plenty of weeds. We moved in the property around 2 years ago but never bother to do anything in the garden as focused completely on renovating inside. Now I've one year old boy and would like to use the garden if possible ASAP, next summers looking at current condition of garden.
I've started clearing the garden bit by bit, so that we can put a new lawn (seeding is preferred due to cost), plant some fast growing shrubs on border.
The reason for growing shrubs is that my garden border is just adjacent to school's playground, and children tend to come in the garden to collect the ball by climbing up the fence or lifting the fence up. We have complained about that to school but no action has been taken. We were thinking of putting some chicken wire on top of fence - high to block their balls coming in but it sounds like expensive idea so moved to shrubs. Will also appreciate advice on which shrubs to go for and best time to put them, as its going to be next to fence and doesn't get much direct sunlight until probably 6 foot high, it gets some sunlight during the day and the soil is really good, well drained. Plenty of weeds growing in the area at the moment to stop children coming in, but they still manage to come somehow as weeds are not very high.
I would also like to know the best way to kill the weeds so that they don't come back again / grow too fast. Obviously like to avoid any weedkillers as wants to grow plants (shrubs and lawn to start with). Some of them have got really good big deep roots which I noticed when tried to remove.
Currently the garden is uneven as well so planning to get around 20 tonne of topsoil to put on top of the current one. Most of the topsoil will only be coming where the new lawn will come. The shrubs side is high already so will only get bit of compost after removal of weeds etc.
Also we have got some good drained claysoil which was moved at the time of extension built, my plan is to use it to level the garden and then putting 150mm of topsoil for lawn seeding. What will be the best time to seed as well so that it can be used ASAP if possible.
While moving the soil I noticed plenty of Spiders (small black kind) in the garden, are they of any threat to us and whats the best possible way to get rid of them, or should I just leave them there, I certainly want this garden to be child friendly.
Will be more than happy to put picture if required. Please let me know if that will of any help.
My budget is very limited but have got good time in my hand due to loss of job.
Just a recap here again.
1. how to kill weeds which are in bulk, throughout the garden.
2. Shrubs to grow once weeds killed.
3. Lawn seeding best time.
4. Spiders in soil specially clay.
5. Child friendly garden.
Thanks again in advance of all help.
As I've mentioned already I'm not an experienced gardener so will really appreciate detailed help.
Cheers RK

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