New Electrical and Heating bundles advice

Try Cosy campers in Rathcoole, Dublin,or VW campers Wexford

Well I suppose there is good and there is better, depends how deep your pockets are!

Heating, Duel Heating water and air for the Hab/area, run on gas / elect.
Whale, Truma, Propex. Research them all to match your fund's
Or diesel heaters. ( big concerns for most would be noise).
If you have room fit two full size gas bottles, use propane ( some will advise underslung Lpg gas system)
Electric. Solar panel as big as you have room for with mppt controer, (wire engine battery into the system) . Twin 90 /110 Ah batteries, an inverter for 220v around 2kw.
Electric hook up, may not be used but don't build without it.
Do a bit of searching around the site, there's a lot of information on solar, ask direct questions most will detail what they have fitted.
Not a great ammoun,on heating, as most have what is already fitted to their m/h/vans. Ask anyway you will get user advise, from people who have changed vans and different systems.
Ignore anyone who suggest generators,

All year round or summer only.
If all year round keep all pipes and the fresh water tank inboard and fit a high level of insulation. Propane is a must because butane stops grassing at 0°C.
If European travel is planned consider fitting a refillable gas system, either bottles or tank, an empty Irish bottle can't be exchanged for a full one outside of Ireland.

You don't say if it is converted part converted or empty van. If you are building look at using as light material as possible so you don't go over the payload