If you have had defaults – it makes it easier to get a loan if the LVR is under 80%.

You can still get a loan if its in LMI (over 80% LVR) territory however that it dependent on a number of things (and this also applies to under 80% LVR loans) such as default type (utilities vs financial institution) amount of default (over $1,000 or under), date it occurred and how long it took to pay it and of course the reason. 

If you have had a default then you cannot go over 90% LVR and the application would need to be strong (good servicing, limited unsecured liabilities, existing customer, etc).

3 units on a single title means a long form valuation and all lenders will want this regardless of LVR. Also with 3 units on a single title there will always be a lack of comparables because of obvious reasons 3 units on a single title isn't as common as your traditional bread and butter stock. The benefit of doing it via NAB is you are doing the valuation upfront instead of submitting the application and praying it that the valuation stacks up.

Also be mindful that you will be up for the valuation fee because it will be a long form valuation (there are 2 types of full valuations). Its up to your broker or banker to see if they can waive the fee but you need to really plead your case. 

Do plenty of ground work before the submission of the valuation. If you can tell me the area I may be able to tell you which valuer to request as we do plenty of 3/4 units on single titles.

Most if not all lenders are now giving little privileges but these privileges don't mean much when their post settlement service is lousy to say the least. They also need to get real with their LMI premiums which are just uncompetitive. 

Whether you get the new loan for the new purchase with the same bank or a new bank is a smaller part of the equation. You really should have an approval in place for the new loan with the assumption that you still have the existing loan debt. There should be no requirement for you to sell the current property. This is what you should be aiming for. 

St George has many short comings but they have pretty good servicing so it may work with them.

Do you have a copy of the valuation? Which lender did you go with? Are the units fully self contained? 

Who is the lender? and why are you not ordering an upfront valuation?

Leave that option as a last resort. Talk to your broker or banker and see if you can service both debts taking into consideration the proposed rental income or the property you are not living in. Who is your lender?

I know is a very different (cheaper) pricing model building in Melbourne and Sydney vs Sydney and Perth. Not sure about regional vic though. Best to engage a builder. I would contact Oscar who posts on this forum. 

depends on the area i.e. state and city. Also are we talking about up and down units or side by side units? How many metres high? Scaffolding is not cheap.

You really need to engage an experienced accountant – lot of considerations other than just transfer of income.