my wife is Belorusan from Brest, I have travelled there several times.
Roads are generally good. Better than many Polish roads and certainly better than Romania. I believe the road from Moscow was built for the Olympics and is in good condition. Most of the main roads in Belarus are in good condition. back roads are good quality graded dirt roads. The road from Brest to Minsk is a good quality dual carriageway or good single carriageway main road.
make a day to visit Brest fortress, very impressive and interesting.
I presume you will be entering Belarus at teresspol. The border can be easy, or a challenge!! depends who is on duty!! It takes from 2-6 hours.
If there is a queue, drive to the front and ask around as many people may be waiting for other reasons (for example there are quotas about how much foreign goods people can bring in daily/weekly so they sit at the border waiting for the time to come round) and as a foreigner on a bike you may get pushed through ahead of others. My wife managed to get 11 motorbikes and my truck through in 2 1/2 hours!! However, when we did the same trip with my parents in their car and us in mine it took 6 hours.
Last time I did it on my own I had to ring my wife for help

. You are given a piece of paper to take around the various stages of border control to get stamped. Once you have a full set of stamps (sorry, can't remember how many) you can go. This paper is then checked by the guard to ensure you have done everything. I got turned back at this point because I was missing a stamp. The guy at the customs post wouldn't help me at all and just left me standing outside. I finally rang my wife, who happened to know some senior officer on the border who then came over from his office and gave the customs guy an earful!! It turned out all he had to do was print a form off his computer in English for me to fill out, but he couldn't be bothered!
Bribes at the border are not possible. There was a big anticorruption campaign a few years back. The police in country can be bribed if necessary. they like euros. They will start high (maybe 50E) but 20 is plenty and you can get away with 5 or 10. frequently I go away with nothing!! For the sake of those that havew to follow, haggle!! bear in mind average wages are low so 20 euros is a lot of money! (my wife earned $160 a month as a teacher) You will need some money at the border to pay duties and for photocopying but not very much
You can buy 3rd party insurance and change money at the border. I think it covers you for all of Russia. Don't even think about trying it without insurance. You will get pulled at some point and if you don't have it, or green card, your in doodoo. Also, you may be checked on exit that you have it, if you don't, again, big doodoo. Changing money out of country is almost impossible (remember belorusan rubbles are not the same as Russian rubles) so change all the money you need to before you leave agin, or you'll be stuck with it. The money takes some getting used to, it's all notes, no coins, and the numbers are huge!!
At the border your vehicle is inputed to their computer system as a temporary import. It must be checked out again. Different border posts are not linked by computer so make sure they know you are leaving via a different border point.
You must have all original documents (vehicle registration etc)
If you are staying more than a few days you must register with the authorities.
The political situation is fine. the exact situation can vary at short notice, for example I have come across restrictions on buying fuel in euros, on buying fuel in rubbles, on duty free etc etc. it changes each time I go.
Avoid talking politics. The big man is not keen on dissent and there are people who will stitch people up. not necessarily you, but the people you talk to. Imprisonment without trial but with a good beating is not unusual for the locals, although foreigners are, in my experience, treated well.
The people are lovely once you get through their initial reserve, they can be wary of strangers. They see very few tourists outside the big cities so as a foreigner on a big motorbike you might as well have come from mars!!
If you need any specific info or help let me know, my wife has family in Brest and if you need it I can PM you my number to ring if you need help/translation.