Buprenorphine's half life is 25-60hrs or something. If you taper down to 2mg or less, coming off it really isn't bad at all. Don't get me wrong, you still get to experience plenty of withdrawal side effects that suck. But it's no where near as intense as coming off a full agonist habit like heroin or oxycodone. The primary difference, of than buprenorphine's withdrawal being a bit less acute/intense, is that it lasts a long time.
When I jumped off buprenorphine, after taking it for two years, and when I jumped off I'd been taking 4mg/day for about a month, the withdrawal was way way manageable. Only issue was I felt this general mailase that it's hard to describe. But none of the stereotypical kicking signs, perhaps other than some insomnia. All I used was temazepam and eventually some gabapentin, and it was cool.
A LOT of it is in our heads, especially with buprenorphine and methadone. Especially when done right, and tapering off after using it for a long period of time. If you can get some comfort meds, or something like kratom, and make sure to taper as low as you can (ideally less than 1mg/day), coming off buprenorphine won't be bad at all. The difficult part will be stuff related to cravings. But that really goes for coming off any opioid.
Since you've been using Subutex for five years a taper is HIGHLY suggested. At least you haven't been taking more than the 4mg/day you mentioned. First I'd split the 4mg you've been taking into 2mg you take in the AM and another 2mg you take in the PM. After a week or two of that, cut down to 2mg once a day OR 1mg twice a day (am and pm). Stay there for at least a couple weeks, ideally a month. Then go down to 0.5mg, and basically stay there for a couple weeks. At that point you can either go down to 0.25mg or just jump off.
With comfort meds like a sleep aid, gabapentin/pregabalin/baclofen, loperamide/immodium, kratom, clonazepam/diazepam, etc., you'll be totally fine and function pretty damn well. If you can keep your head up and have a positive attitude about it all, like focusing on all the awesome things that you'll get to experience as a result of not being shackled to opioids, you'll be golden.
Good luck OP! Did you have any other specific questions?