Advice for buying first boat (trailer sailer)

I've recently become obsessed with the idea of buying a small sail boat with live on capacity (for day sailing and short term 'camping'-type purposes), since realising how cheap they can be found. My context/experience is that my husband and I hired a 30 ft catamaran for 10 days to island hop in Thailand a couple years ago, my husband did sea scouts as a kid, and I am a marine scientist, have an RST and have some experience driving tinnies. I'm under the impression that for sailboats, catamarans are a bit easier to drive, harder to flip and smoother to sail/when anchored.

I have found one on Gumtree that seems to perfectly suit my requirements and what I was hoping to find, a $3000 (negotiable) catamaran, with sleeping space, which appears to be in fully functional condition, but needing cosmetic work. Specifically, this one:
https://www.gumtree.com.au/s-ad/victoria-park/sail-boats/red-baron-catamaran-sailing-yacht-trailer-sailor-/1178687412
My husband says I can have it, but deciding on buying it and fixing it up are all my responsibility.

But, I feel wholly under-experienced to make the decision on whether this is a good purchase, whether fixing it up is within my capabilities, and how much extra money this project is going to require. So, I hope someone can help me with some or all of my questions:

1. How can I find someone to help me look at the boat and make sure it is in good condition (hull, sails, mast, ropes, etc)?
I don't want a full survey as I can tell looking at the advertisement that it's not technically seaworthy as it's missing all the safety equipment, and for insurance valuation purposes I would want to do it up first anyway. I just want someone who knows what they're looking for to give it a once over and agree with the seller that the hull is in "very good condition" and that there isn't anything majorly (expensively) wrong with the mast, sails and rigging. I'd be willing to pay around the $100 mark for around an hour's worth of inspection/opinion. I'm in Perth.

2. Who would I be looking to to "customise the trailer to suit a twin hull", and roughly how much can I expect that to cost?
The boat comes with a supposedly suitable 'licensed tandom break back trailer that will need to be customised to suit the twin hull'. I'm not sure where to start with that one, and I'd like an idea of how much this would cost before committing to the boat. I'm in Perth if you have any specific suggestions.

3. Is a 15 hp motor strong enough for this catamaran?
Keeping in mind that we are not particularly experienced sailors and so it would be highly likely we would need to supplement the sails to make it to places like Rottnest Island (11 nm from coast).

4. Roughly how strong a car would be needed to pull the trailer and catamaran in the advertisement?
Currently we have a Prado but we intend to swap this for either a small 4WD, or a medium-large sedan with towball. I'm not concerned with fuel efficiency, just safety/damage to car.

5. How accurate do you think my cost estimations are?
These are my estimations of how much this project is going to cost:
Start up costs: $3600+trailer mods (purchase boat/trailer $3000, boat rego $250, trailer rego $50, insurance $300, trailer mods unknown)
Necessary safety equipment: $650 (bilge pump, flares, EPIRB, life jackets, marine radio)
Reno/fix-up costs: $1000-1500 (cushions, bed, camp stove, lights, boat cover, +/- paint)
Worst case scenario costs: $1000-15000 for new (2nd hand) motor, $2000-3000 for new sails, $500-2000 to fix major hull damage?

I would love any answers, tips or advice you might have.

1. Try your local sailing club for experienced sailors willing to look at the hull. Or, carefully feel for any soft /spongy patches or evidence of repair - discolouration, rough patches.

2. Try a trailer manufacturer for a top end quote, you might then find cheaper from a metal fabricator. Issue will be where the tyres sit in relation to hulls, and possibly an engineers certificate for mods so you can get it registered.

3. Outboard Weight will be an issue so it's likely that 15hp will be about your maximum hp. This is not a planing hull, so you can't expect high maximum speed, whatever your motor size. A 16ft boat with top speed of maybe 8 knots. You'll feel awfully small midway between Perth and Rotto when the Freo Doctor comes in!

4. A Prado or larger sedan will be fine towing.

5. Realistic starting budget apart from the trailer costs maybe being higher than you have anticipated.

As above, trailer sailors will have plenty of local advice.

This boat has been for sale for a long time. It was listed at least a year ago just before I bought my current catamaran.
Keep this in mind as one day you will also need to sell it. Because is it unusual this may be difficult.
I haven't had a look at it and am unfortunately preping to leave Saturday sailing to shark bay. Wont be back until October.
With what you plan on spending there are quite a few monohulls that are less of project in Perth.
However as a trailerable coastal sailor I can see the potential for this boat.
If you don't have any luck finding someone to check it out with you email me and I will phone you and walk you through what to look for.

Try here
www.trailersailerplace.com.au/phpBB3/ucp.php?mode=register

Im not to keen about the wheel steering and you may have to factor in replacing rigging ,halyards ,sheets etc. Forget cushions etc and use sleeping bags.
Dont forget essentials pp like a porta potti. Forget things like bilge pump use buckets on lanyard. Research boat for things like buoyancy. ie if it tips over will it float.
your budget for safety is about 1/3 of cost ,
eg. Epirb $400

I believe the max width in WA overall is 2.5 . Don't know what involved for overwidth.
sailboatdata.com/viewrecord.asp?class_id=7696