1) With one suitcase is it easier to take a Taxi from Hong Kong International or the MTR? I'm leaning towards planning for MTR, but I wanted some more opinions. How easy is it to find taxis?
For me it would depend on the time of day I am arriving/departing, and how much time I have in HK. A taxi is a short 15-20 minute ride from the airport, door to door. The airport train is about a 15-20 minute ride to Tsing Yi station, where you then have to change to an MTR train to Sunny Bay, which is another 15 minutes each. At Sunny Bay, you then have to change to the Disney train for the final 5 minute stint. From the
Disneyland station, you will then have either a 15 minute walk to the Disneyland Hotel, or a 5 minute shuttle bus ride to either hotel (I wouldn't bother to walk to the Hollywood Hotel, it will be about a half hour walk). It's all very easy and straightforward to navigate, but it does take a bit of time and a few transitions. We still haven't ever taken a taxi (although we should have on our last trip!), so I'm not sure how much one would be, but do keep in mind that the airport train isn't cheap like the rest of the MTR network.
2) On-site or off-site hotel? Like I said, this is my first time going, and just me. On-site seems personally easier, but it seems expensive...
Onsite is definitely easiest. HKDL is nowhere near any other accommodation areas. It's about an hour's commute in from the Central area. Having said that, yes it is expensive. If you need a budget option, it will have to be in the city. You can also consider Auberge Discovery Bay. It's just around the corner from Disneyland, and there's a free hotel shuttle to Sunny Bay station to get the Disneyland train. For us, it was a worthwhile compromise. However, it's still not a cheap option, and you'll be limited by the shuttle schedule (which you have to book in advance).
3) Is 1 1/2 days enough time? My only reference point it WDW, which is obviously larger...
If you're used to WDW, you'll be severely underwhelmed by HKDL's size (and the size of its castle). Personally I find it such a charming place, with so much detail to take in and just a pleasant place to spend time, I could easily spend a couple of days there. However, there are many who claim it to be a half day park, and this would certainly be the case if it was all about rides. There are plenty of character opportunities, including a short line for Elsa and Anna if that's your thing. I think 1 1/2 days is a good compromise.
4) Is there anything you must do in advance? Dining reservations or anything?
Nope. That's why I love it!
5) How busy is it in the summer? Absolutely miserable?
If you're used to WDW in summer, you should be ok. It will be hot and humid, but I don't think the crowds to compare to WDW (especially this year when plenty of mainland Chinese will probably choose to visit Shanghai instead). Think 1 hour waits for popular rides instead of the usual 15 minutes that you get in non-peak season. And you may have to scope out a parade spot half an hour in advance of the parade instead of just waltzing up to the curb and sitting down 5 minutes before the parade starts.
6) Is there a noticeable communication barrier? I can only speak/read/write in English.
There really isn't a language barrier in HK at all, but especially at Disneyland. Most people seem to be able to speak good English, and there is English signage everywhere. The only thing you may have to look out for is the lame jokes on the Jungle Cruise getting a little lost in translation. I would expect much more of a language barrier in Chengdu!
I imagine you'll be having to get yourself used to Chinese cuisine, but if you'd prefer to take a more gradual approach and feel like western style food at HKDL, I recommend the fish/shrimp and chips in Grizzly Gulch, and of course Mickey Waffles!