Road bike? Guessing so from the Sora setup.
Long Story Short
You might need a new chain by 4-5000kms, and perhaps one new tyre.
If you have 8-speed Sora, then unfortunately it's a bit hard to upgrade anything. You're limited by the shifters to 8-speed cassettes and chains, though if a derailleur fails (unlikely) you can upgrade that.
Short Story Long
There are quite a few things that can affect how long different parts last.
Some of your big wear items are:
- depending on the tyre, I've had rear road tyres (700x23 & 700x28) last anywhere from 2500kms (Conti GP3000) to 8000kms (Specialized Armadillo), excluding tyres that have had to be retired due to damage. Tyres will usually wear faster for heavier riders.
I typically retire a rear tyre when the casing is showing through, or when it's getting close to that (profile well and truly squared off) and I start experiencing a few punctures. At this point the front tyre will be showing very little wear, so the front tyre goes to the rear, new tyre goes to the front - keeps the freshest tyre where you need it most for steering and braking.
- again, depends on the pad and also on the conditions you ride in. In dry conditions pads can last many 1000s of kms. In wet conditions I've worn an almost brand new set of stock Shimano pads down to nothing in 20kms. The pads will have wear indicators, so keep an eye on them.
Chains, cassettes & chainrings
- all quite inter-related. Chains get longer over time as metal wears away where the rivet rotates inside the bushing. Gritty conditions can make this wear happen faster.
There's also a couple of schools of thought. My preferred is to measure the chain wear and replace when the chain wear measures 0.75% or thereabouts [*]. If you do this, you'll typically be able to keep using the same cassette for 2-3 chains. If you let the wear get beyond 1%, odds are the chain will have started wearing away the teeth the cassette sprockets to match it's new length. At this point, putting a new chain on will probably result in a lot of skipping, though the new chain will fairly quickly wear to match the buggered teeth. And yep, the new chain will now be buggered.
If the chain get's beyond 1% wear, replace the cassette at the same time.
Chainrings subject to the same worn-chain problems, though they do tend to last a fair bit longer. I'm on to my 7th chain, 3rd cassette on my commuter, and the chainrings are still in good nick.
My 9-speed chains, ridden in all conditions but kept clean and well-lubricated, last about 4000-4500km. My 10-speed chains, probably with less bad-conditions riding, last about 3000-3500kms. Your mileage may vary.
[*]It's handy to have a chain checking tool to measure this, though you can measure with a good ruler. Park Tool make a great tool: