I think an essential for planning is determining if you want to visit the forest, and for how long. The city alone can be seen in two days, assuming you take your time, check out a museum or two, do at least a little bit of shopping, to the river tour. Allow at least one day for a forest trip, including the canopy walk. If you enjoy nature (and it's gorgeous there), find a hotel (limited, and only at the outskirts) and stay to relax. Tour companies have sites and you can spend a night or two in the forest outskirts and see the sunrise/sunset at the canopy walk. Hopefully this provides another set of options.

Whilst I was in Brunei a few weeks ago, I saw some men with long hair in shops and restaurants. Given the publicity around recent law changes, I can see why you’d be asking this but unless a man or woman does anything ‘obviously’ homosexual (kissing their same-sex partner or checking into a double bed room with them in a hotel) then hopefully you won’t have any problems. As for entering this mosque, tying up your hair might be a good idea to avoid suspicion or derogatory glances/remarks. A sad state of affairs I know but probably best given the country’s laws.

They will have gown for you. Don't worry.

of course you can visit,solo, but dress correctly and not during prayer. you can take a public bus from bus station downtown, stop in front of mosque.

If you come in the above mentioned clothes, you can borrow clothing at the mosque to ensure you are appropriately covered.

Hello, from the Kianggeh Market (open market) it would be about 15 minutes drive from Jame'Asr Hassanil Bolkiah Mosque. On the other hand the market is about 10 minutes walking distance from the Omar 'Ali Saifuddien Mosque.