If avoiding crowds is your biggest goal, being there within a few days/weeks of Carsland opening is not going to be ideal. Until about the third week of June, Seasonal Passholders still have access to the parks at least 4 days per week. This leads to a tremendous rush of locals visiting the parks before they are blocked-out for the rest of the summer.
If Carsland does open in early/mid June, yes you will be ahead of the summer wave of tourists. But Passholders looking to experience Carsland before their passes are blocked out for 2 months will absolutely mob the park. We spent some days at DL last June and saw 3 hour waits for Star Tours and 2 hour waits for the new Ariel attraction.
Summer does see an increase in tourists but with the Seasonal and Deluxe blockout dates, crowds are typically quite manageable as long as you avoid major holidays.
In short, if Carsland opens when Seasonal passholders still have access to the park in June, IMO the crowds will be FAR worse than a typical non-holiday period in July or August.
Thanks for the advice. I hate to admit it, but the main reason I made the reservation was that I have a June UY

so its very easily cancel-able, and we aren't using our points for a big VGC trip next year since we are going to the World instead. Then we weren't planning on buying AP's but it turns out that we ended up spendng 9 days in DLR this month, so we have Deluxe AP's now. Therefore all signs point towards us taking at least one weekend trip, preferably after Carsland opens, since new is always fun though we'd be happy getting our Disney mid-year fix even without it being open. Love that owning DVC allows us to 'play' with our points this way.
The other main reason we wanted to avoid late June is that we really like May & October weather, and the later one gets in June the more likely one is to run into heat _and_ crowds.
This year we were there for the CM & AP lottery previews of ST & LM, though our CM friends did not have enough extra passes for us and we did not win the lottery tix. To see ST on the first day, if our schedule had permitted I'd have been okay with braving the mob for one day, then maybe switch over to DCA/other parts of DL which were not as full from people's reports I was reading on the DLR board. So for this trip, if Carsland is open, we'll probably brave the mob one day then head over to DL the rest of the weekend and spend some time at the resort too. Also its possible that the on-site DLR hotels might have a similar promotion with fastpasses for new attractions only, if it attracted enough business for them this past year.
Alternately we might cancel the reservation altogether and stay offsite, change the weekend and waitlist or stay offsite, or whatever. Just have the reservation there as a placeholder in case things work out so that is a good weekend for us to enjoy our home resort & getting a little more use out of our AP's. Not putting a ticker up yet since its all tentative ... finishing my Master's in several weeks and though I love my current position, still hoping to find a better job a little closer to DL than 2.6k miles and move, so everything for us for next year is kind of up in the air, particularly mid-year trips. So Disney is allowed to be up in the air on Carsland too.
Apologies, for saying in a really long winded way that the goal is more than avoiding crowds, and we have reasons it works for us that may or may not apply to other people, but thanks for the crowd warning!