At the time of my trip there were about 2.8 Malaysian Ringitt (MR) to the USD and gas was about 0.52 RM per liter. ATMs or cash machines are widely available. I did not take anti-malarials but carried enough to treat myself if I got sick. I did not get sick. Public transportation supplied most of my needs without pre-booking, and only in the Kinabatangan River area did I find it inconvenient not having a car. The Sabah Tourism Board in Kota Kinabalu (KK) was very helpful with maps and logistics. The Lonely Planet Borneo guide book was useful for hotel phone numbers and basic travel information, though hotel conditions were often different from those described. I bought a cheap (80MR) Nokia phone in KK which cost 30MR per month to operate with Celcom, reputedly the company with the best coverage. In-country rates were very cheap and I never used the full amount of RMs it took to keep the phone running.
My route took me from KK to Mt. Kinabalu, and then Poring. From there I circled back to KK before heading to Sepilok, Sakau and Billit on the Kinabatangan River, Tabin, Semporna, and Tawau. Total drive time from KK to Tawau by way of Semporna in a private car is about 12 hours. Roads were in reasonable shape, mostly paved though with the usual poorly flagged areas of construction or missing road. Though most drivers obeyed traffic signals in towns, speeding and passing blind were not uncommon on mountain roads. Note that if you are heading to Mt. Kinabalu or the Crocker Range for early morning birding, you will likely be stuck behind the ice trucks that go very slowly up hill at this hour.
Bus drivers were generally cautious, but being in a bus after dark was a bit scary; at least one fatal crash of the all-night bus to KK occurred during my stay. Because they were convenient, I often travelled in minibuses; large vans with 4 hard seats and little leg room. Great for distances less than 2 hours, like from Semporna to Tawau, or KK to Mt. Kinabalu. The express busses were nice, clean, and comfortable with reclining seats and bathrooms. Be warned though, they crank up the a/c to the point where icicles form on your eyelashes and play hideously amusing Indonesian movies at full volume. I carried a fleece jacket and earplugs. First class seats (downstairs) were larger and less noisy, though still very cold. Watch where your bag is put in the luggage hold, and try to get it set on top of something like the spare tire. Even if a bit dirty, it may save you having the entire bottom of your bag soaked in smelly goo from the leaky fish boxes. My bag still has a faint perfume. The bus company with the logo of a horse (can’t remember the name) is reported by locals to have the best safety record.
I used Phillipps and Phillipps (2011) as my field guide because the plates were easier to see and grouped for easy comparison. I found the biggest limitation with the book was that it didn’t include much text regarding identification. I carried Meyers (2009) in my luggage, and used it as a backup when the P&P plates and descriptions were lacking. Because both books are relatively small (relative to say, birds of Ecuador), this was a fairly good arrangement.