Buying a new Pop top

I'd suggest getting alone to a few sales yards and having a walk through lots of vans to see what you like (people like different things) then when you find something, pop back and ask specifically about that van (whether people have had issues, etc).

Also, adding what you want to do and where you want to go is an important factor. Some vans aren't suitable, others are overkill.

Some starting points:
1 Pop tops vary so much, but start by deciding what you really need in terms of the basics (how many beds; what seating; what sort of kitchen (oven? microwave? Size and type of fridge)
2 Decide which you prefer: light weight European style black top style; traditional Oz style black top van; Dirt road van (often called ‘off-road’ which they aren’t); true off road van (the heavier style like Bushtracker etc.)
3 Look at various vans, and make you mind up about things like the amount of light (the more windows, the more light of course, but the fewer the windows, the less heat gain/loss, and also the more scope for storage cupboards). We found many vans to be claustrophobic, especially some of the dearer ones.
4 Assess the various brands for quality and price (lots of talking, especially to owners, and not too much reading of nonsense articles in the mags).
5 Pay close attention to the technical stuff: especially Tare mass and ATM. Don’t be fooled by brochures, and make sure that the REAL Tare is stated as well as the REAL ATM. The difference is the true payload, or the total weight of all your stuff (utensils, bedding, food, personal stuff, etc.). Some vans come close to ATM with nothing in them.
6 Look at sizes of vans as well as weights, and compare with your tow vehicle’s capabilities (mass and drawbar loading). Leave a margin!
Hope this helps

Get out in your tent, look for other campers with rigs that interest you and ask. You'll get lots of first hand info from the owners themselves - far more accurate that from a dealer, and most people are forthcoming with the pros and cons of their rig and happy to show theirs off. They will also tell you of any problems if encountered far more freely than they wil put this info on the internet.

Motherhen

All good advice so far. I suggest two things to look at carefully.
The bedroom - double or twin? Twin beds will give more floor space making the van look more spacious and can be used as couches to provide seating. This could be useful when the three of you are all inside and one is trying to prepare a meal! The weather will not always be good. Many smaller poptops have twin beds. A double may give more storage space under, check this carefully - some manufacturere fill up your storage space with batteries or other stuff especially under twin beds.
Consider two bunks so your son can take along a friend in due course. Some vans have a top bunk that folds away when not in use to leave a couch.

Kitchens in vans are sometimes useless. With a family you will want to prepare most meals unless you are very rich! You need some bench space. A laminated cover for the stove gives a useful surface - better than glass. Otherwise look at the arrangement of sink, stove and fridge. Are they grouped so as to leave usable and convenient bench space, even if small or do you end up with useless spaces between appliances? Also you will need somewhere to keep saucepans etc without them rattling around - a pot drawer is great to keep them under control. We have found this more useful than an oven but that is a choice to consider. Is the location of the stove likely to cause a hazard for a child going in and out of the van?

I hope these ideas help you when you are starting from scratch. You will soon start getting your own preferences sorted out.

Buying your first van secondhand can be a very good idea. It saves money up front and you lose less if you later change your ideas and upgrade as you get more experience!
Have a lot of fun! That is the main thing! Lynne