My furcation = need implant. Previous bone surgery on front lower teeth extremely invasive--a 10 on a 10 scale. What is a molar implant on the scale?

Relatively pain less. Most patients report feeling less discomfort during and after implant surgery than in periodontal procedures.
Talk to your dentist. An extraction is more of a postoperative problem than placing an implant you don't say if the implant will be placed at the time of extraction but in any case bone will need to be placed either first or at same time of extraction but both procedures shouldn't be painful procedures.
Implant surgery. It depends on your pain tolerance and the type of implant placed. Bring any complications should be able to control your pain with otc medications. Without knowing what exact type of dental surgery you had before it is hard to compare. Discuss your concerns with your dentist. The implant will benefit you. Good luck!
Depends on surgeon. I have been placing implants for almost a decade and i tend to find that extractions are usually worse than placing implants. I'd say yopu should have a 3-5 out of 10 depending on if you need bone grafting or other procedures done at the same time as the implant.
Surgery is invasive! All surgery is invasive. So too is an extraction. If you have an ideal, healthy implant site with plenty of pre-existing bone in the right location, an implant can be far less invasive than an extraction. Consider staging your implant. Remove the infected tooth and simultaneously place the bond graft. Then, four months latter, after the site has healed, place the implant.
Lot less. The pain you experience following any surgical procedure depends on several things. 1. Your pain threshold tolerance 2. The health of the surgical site. The less infection the less pain 3. The skill level of the surgeon and 4. Time. The less time it takes to perform the procedure typically the less pain.
Depends on lots. Typically, around a 3-4. Often far less. It sounds like you may be very sensitive overall, so your response may be higher. The discomfort / pain is a result of tissue manipulation, anesthesia injection sites, sutures, and the overall tissue sensitivity after surgery. He bony aspect is not a factor as such. Most patients take nothing more than ibuprofen. You may be sore and uncomfortable. Not 10.
Not difficult. Generally dental implants are less difficult and less painfull than periodontal surgery. Placement of an implant in any healed site takes no more than 15 minutes, with no cutting, no stitches, no swelling and little pain, just some soreness.
Hard to say, for you. Implant surgery is usually not painful. I have placed over a thousand implants with only local anesthetic and not one complaint. You should consider sedation so that you are asleep when the surgery takes place. All the best..