Mate i would reccomend with your tech toys to stick with furuno its tried and tested and wint let you down charts i would buy the navionics app on your phone and also buy the best card navionivs card you can afford for your sounder this is a really good thing to have then 180ltres for a 225 ho outboard im not sure that that would be enough i have a 150 merc and we have a 200lt tank sight seeing carnac island is a great spot go i  close drop anchor and have lunch and you can see a few sea lions lazing on the beach also rottnest of course is another spot.

Hope this helps good luck

 I’m in the same position mate looking for a some new electronics, got the Furuno as my sounder just want something for the chartplotter side of things! Have been looking at the Axiom aswell they seem like a good unit! But between these two aswell, Garmin 952 or Simrad Go9 just can’t make a decision on which one I prefer !! 

 Can't fault my HDS9 gen2 for a chartplotter. I run a furuno 585 with 1kw tranny so that pretty well covers it all.

 Yeah sea-kem sounds like a good setup mate!! just the new Carbon is a few more dollars than the ones I was looking at!

 I run an ipad with navionics App installed on my Bar crusher, Cant beat having the big screen of the ipad and does the same job as a expensive plotter then you only need a dedicated sounder. As for sounders go the best you can afford as youll always want to upgrage if you go a cheap one........ 

Rotto is great for exploring and nice and close if you pick your weather but can easily run home when it does blow up.

Track your fuel usage and you can then work out how much you would need to do the Abrohols islands....... you can get a bladder made or just carry jerry cans to get and extra 100 or 150 litres of fuel onboard pretty easy, but the key if working out how much you use in different conditions so you can be confident youll not run out. long way home with a paddle :-)

 Great boat purchase.

I have an Axiom Pro 9 now with a dual channel chirp 1kw transducer which I'm still getting used to. The sounder and plotter is quite good. I've had a Simrad Evo3 7" which was also very good, I also think the Garmins look really good too. I chose the Raymarine because of the following

Has two 1 KW channels as well as the side, down vision, 3D and high chirp channels for sonar. Has a very bright screen but not quite as good as the Simrad. Has button and dial controls as well as touch screen for when the screen gets wet or the conditions are crap and too bouncy for tough.

The software in the Raymarine is still a little raw compared the Simrad and Garmin but the Updates are coming and I'm confident this unit will improve.

I've tried the 10" tablet with the Navionics app and although it works pretty well, I found problems with water resistance, battery life even while connected to a charger and generally just reliability in a marine environment. Good as a back up though and worth installing on your phone..

I imagine you could make the Abrolis on a boat like that if the weather is right and you plan well.

I have converted from Furuno to Simrad a few years ago and have never looked back. The new gear they have is so easy to use in auto and so much better when you dial it in. Very user friendly. The new evo3 are dual ch 1kw and the s2009 are single ch 1kw. All depends on what you expect from the unit such as deep water or shallow reefs and how much you want to pay.

Used to fish Abrolhos when I was in Gero and a mate would take his 4.8mtr quintrex over on good days. Pick the weather and you will have no worries. You just need to identify your safe fuel range so you dont run dry. Most I ever used out there was about 120lts from a 175hp suzuki. You should get about 1lt per km from the honda depending on conditions. You can always carry a fuel bladder or jerry cans for longer trips.

 Mate has the same boat, these are strong WA built hulls. No stress going anywhere in whatever ocean. Even been a drift missing from onslow to barrow island for 2 days still intact.  180L for 225 is plenty, i have a 250 suzi and still only use 100-130L with 180L tank on a big day on water. 
Sounder, go furuno if you're more into fishing and not worried about maps, go with simrad/lowrance if you're more into better maps and usability.
Sightseeing comes with more time on the water. Past week i've seen penguins, turtles and dolphins. 

Thanks for all the comments.

I'll look again at the Simrad/Lowrance/Furuno ranges.

I am keen on have an 'All in one' unit as opposed to seperate sounder / nav units

Started thinking about whether it is possible to put in a long range fuel tank, and also a bigger kill tank.

 You'll find you will be doing a lot of page changing and menu hunting ( although this varies with make/model, touch is better) --you often have to go to the specific page ( sonar or nav) to get context-sensitive menus. And your real estate is more limited.