Is buying new a priority? Fibreglass good for family, Ali better for fishing layout - you will use the boat 90% of the time without family and when you do, you only go when it is calm - This is my experience of having 3 kids. I have a Buccanneer Billfisher that I love and can handle everything I use it for - bar crossings, going wide or softbaiting shallows, but this is my 4th boat and I would recommend something smaller for your first boat. 
Therefore, my recommendation would be the 1550 or something similar - 5m Senator etc. Get some bean bags for the kids to sit on down the back of the boat and get seadek type flooring to keep it better on your feet for the family. Wouldn't be keen to take to GBI, but as you have more experience and confidence, you can then upgrade to something bigger

Great summary there Letsgetem. I agree on the 5m boat too, I wouldn't take one across to GB

if having wife and kids with you on a regular basis is a priority - fibreglass with a cabin and canopy is the format which is most likely going to ensure success. 

Start smaller and stay local for a while.
That stretch of water by the barrier can get really nasty really quickly. I have a nervous to in a heavy 6m boat a few years ago.
Don't underestimate it.

For other fiberglass options in the 5M bracket - i would also look at haines hunter 545 (better layout that 535 HH), Sea Force 530 and buccaneer 525. They all ride well and in the order I have written, good enough layout for fishing and decent cabin for family. work well on lake and look good

Yea.. all good advice roz.

Realistically the kids are probably too young to to take out for too long. My vision is taking them out with enough food to get through the day, putting them down for a peaceful nap on the cuddy around lunch time, island hopping and exploring in the afternoon reality is probably tantrum and tears as soon as boat has launched, sucking it up for a bit before heading back miserable 45 min later.. drowning in my sorrows with a bottle of wine... perhaps your right.. maybe you're onto something bugger kids and get the 1550 fisher ;) .. going to make getting a pass from the wife harder if I can't take one or two of them with me though

I suppose it depends on how much you want to keep that first boat. Whatever you get, just make sure that there's a way to get the sun off the kids. If going West Coast, you won't be bringing kids for a while. I'd rather have a Stabi or similar for bar crossing than a glass boat of the same size. 

Im pretty much along the Bounty Hunter comments.
5m is just that little bit small, hull length and cramped for over the bar, the chop outside and makes a trip to the 60m and barrier a long long one.
 And if chopps up for return home...

We spent the last near 10yrs out on the east coast , bottom end Waiheke, Firth, Coro in an older  5.5m glass with over nighters.
 Now moved it is Manukau Harbour and the west coast bars.
Ideally I think a alloy maybe better, but in saying that the old 5.5m does real well, in harbour and river.
A 6m or 6.5m hull (which currently thinking about going to) gives better  comfort options on the bars and out wide.

5.5m would be the smallest would go.. Barrier trip will have to be carefully planned for the barrier. As with bar trips.
 And even then that trip out to 60m with a little chop and 1m swell drags out abit .. Cruising 19/20 mph. Mirror day 30 mph.

 As for solo launch, a little thought, a 5.5 m is NPs at all, even on a keel trailer.. Even in a strong side wind or current... and dont put the trailer too deep.
Going up in size, a Buccaneer 635. would be far more ideal concept type boat for your longer term use.
Barrier far more do able in comfort. Solo launch NPs

 Another issue is well powered.. on a bar, when that pair of 'freak waves' climb up in front, even on a 1m swell.. u NEED that power..
How a hull performs, comfort , speed , and helm control, in chop is determined by the amount reserve power at the prop at that speed.
General 5.5 m cabin around 1200kg total gross weight on water about 130/140 hp
 6/6.5m 1800/1900   200hp

If was me, a small family, spend bit of time east coast, thinking hit the barrier on a good window. Spend time on the manukau with odd trip over the bars.. would go FG, around 6m+
 If a west coast fishing machine, would be a flip of the coin on alloy or FG weighted a little more to Alloy, again 6/ 6.5m

Boats are like planning out a garden or choosing a  tropical fish tank or making a garden pond.
 Mark out/ choose tank size, then increase by about 1/3 and you will not have the need to re do/ change later.

Another good perspective steps.. this is the post I want to hear. But probably not the post I need to hear as it brings the expensive 6m plus boats back into the mix!

Order sight unseen
1) seaforce 530 mate
2) fi glass firestar/senator
3) 1550 fisher
4) f it.. all in on a 1850 or 2050!

Order changes with the wind and each post at the moment! All good advice though...

And the practical realist answer that brings something like the 1450 explorer into the mix. Probably a boat of this size is most sensible starting point... and still a lot of fun to be had...