1) I have the opportunity to go to Perth with DH's work, we'll be flying there and back, but we used to take a taxi to the airport before we had Keenan - what do we do now??? YAY I am sure you will love Perth, it is a beautiful place to live and visit!!! You can still catch a taxi, especially if you plan on taking your own car seat away with you. They will make sure that the taxi has an anchor point, well that has been my experience so far!

2) I know he's only four months old, and I expect he will sit on my lap, but do they have a special seat-belt or does he 'use mine' What's the deal there? Would I be better off putting him in his sling? If you put him the sling you will have to take him out again. There are special seatbelts you have to put around them that connect to your seatbelt. From what I understand you are not allowed to have your baby in the onboard capsules during take off and landing.

3) Again with the car travel...If we're hiring a car once we get there is it better to take our own car seat and ask for a car with an 'anchor point' fitted? I would take your car seat if it is not too much drama, most car rental places hire out carseats but who has used them? Just my thoughts and will make your trip easier because you wan't have to get used to the new seat etc...

4) Should we take our own port-a-cot (he likes it...) or is this too much to take along with everything else?
If you really want to take your port-a-cot then do it. Bearing in mind that if you take your carseat and the pram you will have the cot and your luggage on top of all of that. Most hotels do rent out cots and the are usually in good condition.

HTH

Cheers