Getting to Chachoengsao from Bangkok is straightforward in a few different ways, which is one of the things that makes the resort a realistic option even for visitors based in the capital. The State Railway of Thailand runs regular services from Hua Lamphong station to Chachoengsao Junction, the journey takes about 1.5 hours and costs almost nothing, and arriving by train into a provincial Thai station has its own particular pleasure that is very different from arriving by road. From the station the resort is a short taxi or songthaew ride.
Driving from Bangkok takes about 1.5 to 2 hours depending on which way you leave the city and how badly the eastern expressway is behaving - the Bangna-Trad highway is the most direct route and is fine once you're clear of the Bangkok sprawl, which admittedly takes longer than the map suggests. Having a car in Chachoengsao makes the stay significantly more flexible and the resort has parking that handles it without complication.
From Suvarnabhumi Airport the resort is actually quite well positioned - the airport sits east of Bangkok and Chachoengsao is further east still, meaning travellers arriving or departing from Suvarnabhumi can connect relatively directly without having to go into the city first. The drive from the airport to the resort takes about 45 minutes to an hour in reasonable traffic and it's worth knowing this if you're building a Thailand trip around a Bangkok base because it changes the logic of when to visit.
Getting around the Chachoengsao area once you're at the resort requires either a car, a motorbike or negotiating with local taxis and songthaews for each trip - there's no Grab saturation here the way there is in Bangkok, the app works but coverage is thinner and wait times less predictable. The resort can arrange transport for specific excursions and for guests without a vehicle this is the most reliable approach rather than trying to improvise it independently each time.
Public transport within the town itself is workable for the main riverside area, and the weekend market is accessible enough that not having a car doesn't prevent you from reaching the best thing in town. But for the temples outside the center, the provincial countryside and any serious regional exploration, a vehicle of some kind is the realistic requirement rather than an optional convenience.