1 week in Tonga... Tongatapu AND beyond?

I would certainly suggest getting off Tongatapu if you have a week in Tonga.
If flights seem too expensive for you, Eua could offer a more cheaply accessible outer island experience closer to the main island.

Thanks for the advice. Looking into it quite a bit more, Ha'apai sounds real appealing. I'm only worried about the situation with flying Real Tonga. I've read some pretty serious complaints about them as recently as September 2013. Have they improved at all since then?

I wouldn't know, but if planning such a trip, it is probably best to fly to Haapai first and leave the few days on Tongatapu for the end to allow for delays and cancellations when flying back to the capital.

I'll arrive on a Saturday at 10am, and I see there's a flight leaving for Ha'apai on Saturday at 2pm. I've heard that Real Tonga can change flight times w/o notice, even moving them up earlier in the day! Is it wise to try and fly out to Ha'apai on that Saturday or should I just wait til Monday? Also, I assume the international and domestic areas of the airport are next to each other and only a minutes walk away?
Thanks again!

If I were you, I would try and book that flight.
Hopefully it will take you on that day, or if not, they put you on the next available one.

Unless diving/snorkeling is your main thing I'd recommend Vava'u over Ha'apai. Ha'apai is flat and boring compared to Vava'u which is larger with hills lots of small villages and a pretty harbor. There are lots of good places to eat. Ha'apai (actually Lafuka Island where you'll land) has few places to stay and is more expensive, both to eat and sleep.

Also... the Real Tonga terminal is not a short walk from the international terminal. Especially with any luggage. Just take a cab ride over there. Negotiate the fare first. Don't pay over $10 TOP.

I was there in September and flew RT to both Ha'apai and Vava'u. The Chinese MA60 pilot got sick with the flu and was unable to fly for two days. They had to make five flights a day to Vava'u with the smaller Islander and Beech aircraft ,normally used for the smaller islands, to make up for the grounded 50-seater MA-60. That messed up the Ha'apai flights and stranded some people there. Some ended up taking the ferry back to Nukualofa.

By the time I left in late September the place was crawling with Chinese trainer, advisers and observers. In the meantime the Tonga Minister of transportation told the New Zealand air transportation officials, who had declared the Chinese MA-60 unsafe, to take a hike. New Zealand has cut off $10M in aid to the Tongans.

Now Tonga is in bed with the Chinese. And the Chinese have announced a plan to provide aid and is giving them two additional new Chinese Y12 aircraft to supplement the MA-60. The two Y12s are smaller than the MA-60 and will probably replace the old Beech and Islander.

The success of Real Tonga is real important to the Chinese who are trying to break into the airplane building business. They'll probably make Real Tonga Air a showcase for their airplanes. They are already throwing a lot of money and resources into the deal.

Thanks again for the advice!
I'm glad to hear that Real Tonga at least seems to be trying to get over their growing pains.

How far of a walk is it from the international to domestic terminal? I don't plan to have any big luggage (just backpack probably) and if I'll have quite a bit of time in between flights, I think I'd rather spend it walking between terminals than sitting around waiting.

I am kind of keen to get away to a less touristy area and do some snorkeling and/or kayaking. How boring could Ha'apai be? and how much time would you recommend for either Vava'u or Ha'apai?

Cheers

I, for one, enjoyed Haapai more than Vavau.
Much more laid-back and less touristed, with far better beaches and more islands accessible by public transport or even by walking.
And I actually found my cheapest homestay accommodation in Tonga there.
Also, great offshore snorkeling at Uoleva.
The 3-4 days you would probably have there would be very easy to fill.