Riding Indonesia!

[Green_Jinjo]

Hi HuBB,

I'm leaving on my third big trip in my life soon and I'm super excited to get going! The first leg will be Indonesia, I'll be there mid March to June. It's a mixed bike and surf trip.
For the bike part of it, I plan to travel
1. North Sumatra
2. Bali, Java & Sumba
3. Timor

Buying a bike and doing it all continuous is not an option, so for each of these locations, I'll need to rent a bike. I'd therefore like to ask two questions:
Does anyone have a recommendation on where to rent a decent offroad bike? I'd be looking at 250cc bikes, something like a CRF 250 - but I'm also happy with a 150cc bike if there is nothing else available. I don't necessarily plan on riding hard dirt anywhere, but from past experience in Indonesia I love the confidence the bigger engine and longer suspension gives compared to the scooters.
For Sumatra, Medan seems to be a good starting point, and I have found this vendor which has a decent selection of bikes- but they are, for Indonesian standards, quite expensive to rent: https://www.mahongrentalmotor.com - so I'd be happy to learn of any alternatives.

And, does anyone have riding recommendations for roads to take, especially in North Sumatra? I plan on climbing volcanoes, visit lake Toba and so on, but I'd be happy to get any more specific biking recommendations on great drives, be it on road of off road.
Thanks in advance!