Fix the brakes first. Any vaguely competent mechanical mate will be able to show you what to do. New pads and disks on the front take about 30 minutes a side and are very easy. Rears a little more fiddly, but if you have a caliper windback tool, again very easy. Getting a garage to do it? Between £250 and £500. This job always costs a fortune at garages. Don't know why.
Suspension - a bit harder. The drop link is easy and the part costs £15 or so. The upper arm is pretty easy, and from memory, the part costs about £70 for genuine, less for pattern. The lower arm can be a complete b'stard to replace, and costs about £120 or so. The rear arms are easy, about £20 each. The only downside is the rear hub locating bolt, which can be another b'stard, there are several threads on here....
As you have to get the suspension reset after fiddling with it, best to get all of the suspension jobs done at the same time. You're looking at a grand or so to get all this done (both sides) at a specialist, might be cheaper at your end of the country.
Air filter - as long as it is not leaking air, and won't fall onto the road, fix at your leisure.
I'm winging it on the parts prices, I did most of these jobs a year ago. Shop4parts is a good source of parts prices.