FHB PPOR as a duplex – FHOG eligibility, tax deductability of loan, one or two loans?

Hi there,
I am wondering if anyone has some experience or rock-solid knowledge about building a duplex as your first home where you are eligible for the FHB grants of $21k

Why am I thinking this? I am very keen to get started on the property investment trail and figured that if I could combine my first home with a separate investment property, perhaps I can have some cake and eat a little too.
Note: Plan B is to continue with the single dwelling to live in and buy a second investment property ASAP. (But I really don't like the extra transaction costs that will come with it.)

Background;
Settled on large size block of land that is zoned for single-dwelling and duplex.
Average rents in the area for 3 bedroom house/townhouse fetch $280-340 per week.
Pre-approval to borrow up to around $500k for FHOG/FHB on the house. (Looking at spending a maximum of around $400k)
Have 20% deposit.
Would look at living for a few years in the PPOR then renting both out whilst purchase or rent somewhere else.

Questions;
1) Is there any reason why the grant ($21k) will not be paid because we are building a duplex rather than single-occupancy dwelling? (I read the eligibility criteria from the government and it does state duplexes are valid residential homes, but it is too vague to tell if that includes building a duplex where you reside in one side and rent out the other)

2) Tax-deductibility of the interest payments on the portion of the duplex that we rent out as an investment? (this is particularly confusing because in effect, one side will be our PPOR, the other side will be an investment property)

3) Does this go all under one loan or two? i.e. One loan for the PPOR, the other for the investment property. (Planning to discuss with my mortgage broker tommorrow)

3a) If the loan is split in two, how are they portioned and do I hold it all in one name? (e.g. As opposed to putting the investment half in a trust, although I have no idea if this could even be done)

4) At a basic level, is this even a good investment starter path? (In my mind it is, but I may be thinking too simplistically about it)

The more I think about it, I probably need to talk to an expert. If anyone has advice in the meantime, it would be very much appreciated.

Thanks,
Emptyvessel