We rented a car last year for about a week and drove from Heraklion to Phaistos to Hora Sfakia to Elafonisi to Chania and points in between. One week allowed a good amount of time to see sights on the western half of the island and visit both cities and countryside. The quality of road surfaces and signage is generally very good on main roads. The main highway running east-west between Heraklion and Chania is several lanes wide; we experienced cars passing each other in 'creative' ways and just kept an eye on that. On our agenda we were always hitting the highway in late afternoon/early evening; traffic was no problem. The other largest roads on the map were like curvy mostly one lane U.S state highways. It seemed like we got off the beaten path a few times. E.g. in the higher elevations sometimes the roads hadn't been cleared recently of rockfall so you need to keep an eye out. Some times there are no guardrails next to sheer drop offs. Crete has more live animals in the road than anywhere else we've experienced, including sheep, goats, and dogs just lying in the road asleep; never did figure out that last one : ) There are a lot of blind corners that narrow to a lane or lane and a half. In general driving in Crete requires more focus. My husband is a confident driver and really enjoyed the experience. I am a less confident passenger : ) We're both glad we got to see a lot of the country because it is varied and has distinctive areas. Crete is really beautiful.
We didn't find ourselves in tight parking scenarios like we have in Portugal and Spain; we avoided driving in Chania and Heraklio which probably helped. In Heraklio we picked up on a Monday morning in the city center and it was easy getting out of the city and heading south to Phaistos. In Chania we dropped the car at the Souda airport on the way into town because the rental agency was open later, and took a reasonable cab into the city center. We were occasionally on challenging inclines, particularly in a couple of hill towns. You might want to consider that in terms of the rental car.
I read in a Crete guidebook that what looks like a short cut usually isn't. That was our experience. Some of the smaller roads on our map were one lane, slow going and twisty. The seemingly longer route on a larger road is usually the better choice, unless you're up for a bucolic detour.
I posted a trip report last year here on the forum if you want to see our itinerary in more detail and see what we did in about a week, including what we would have done differently. In all we really loved Crete and found it and it's people very charming.