Snoopy is absolutely correct. If you're not very capable mechanically you definitely need to find someone who is. I'm a mechanical engineer and knew what to look for, but still managed to shred new drive belts on belt changes twice. This is an expensive car if you get something wrong. (and I bought mine very broken from licensed mechanics who still got it wrong)
It's a beautiful machine. Since you've bought it at 100,000km, if you do a transmission fluid flush (and I don't mean a drain and refill) soon and reflush every 50,000km or so the transmission should give you no real problems. The refill procedure includes knowing the transmission fluid temperature, for which you really need a Volvo scan tool.
Engine oil and filter changes are the same as any other car (once you have bought the filter housing tool), but please do them every 10,000km with quality oil...15,000km intervals are way too long.
Your main maintenance will be coming up at 150,000km - at that stage the engine will likely be gushing oil out of the timing cover and cam covers (if not already ?). The seals themselves aren't stupid expensive (and the best clue here is source parts overseas...FCP Euro, Volvopartswebstore etc are much cheaper including shipping and the Sydney dealers couldn't source basic engine parts for the V8). This is a difficult job for most mechanics to get right and you'll need to find someone who knows what they're doing.
At the same time, replace all of the idlers, tensioners and drive belts. The idler or tensioner will let go soon after 150,000km and likely take out the timing cover - which will mean around $4000 in repairs assuming you haven't ruined the engine in the process. (The tensioner has a hydraulic damper which is uncommon...and forcing the tensioner too fast to release the belt WILL cause the tensioner arm to break off which will eventually break off prematurely. 3 out of 3 I have worked on had this part broken when purchased.
The front struts and control arms will be nearly dead around the same time. Changing struts, mounts and control arms will renew the handling. Rear suspension doesn't generally need anything.
What to check on pickup ?
Does the AM band on the radio work ? (Many fail, and it's very expensive to fix...)
Does the drive shaft to the rear diff turn when the car's stationary ? (ie you will have no AWD functionality - stripped coupler splines are less common on the TF80SC transmission models but still possible if someone's enthusiastically used the V8 power offroad...)
Has the belt tensioner arm been snapped off ? (Can see in engine bay if you know what to look for)
Does the fuel filler flap lock correctly (every one I've seen has been disconnected because they couldn't be arsed spending 10 mins to fix the lock), or flap in the breeze ?
If you have a sunroof, the blind will slide back and forth by itself...but mainly check the drain channels down the A pillars.
Are your front seat switch panels on the squabs cracked ? Once again buy from USA, being careful to remember they drive on the wrong side. The Oz dealers wanted hundreds, but because they were such a failure item with oversize Yank arses the parts were made available really cheaply over there.
That should be all I can think of for now. Don't want to put you off, mine at 320,000km is still running the original coils and injectors, and hasn't needed anything but routine servicing , It's dead quiet and smooth and I think it's one of the best cars ever made. However if your mechanic doesn't know these cars they will cause more damage than good.
All the best. The car looks fantastic.