1.) Our golden is a male and neutered. Will there be any issues long term between the two if the doberman is a male as well.
This has been addressed, but I'd like to echo: don't take the chance. Get a bitch and save yourself the grief.
4.) How do i feed two dogs with no issue? I'm guessing the baby will learn from the older one, when it snips at him, if it becomes an issue.
Crate feed for safety. This forces the dobe to chill before and after meals (important with a deep chested breed, for bloat prevention). This prevents food theft, and protects grabby kids from digging in food bowls. This also ensures there's no competition between them. Set a routine before puppy comes home, to get your golden used to it, and stick to it. Twice a day, crate feed, leave them there for a little bit to let meals settle, then release them from the crates.
5.) what is the best age to start with a trainer?
Immediately. We brought Ripley home on a Wednesday and had her in a puppy prek that Saturday.
6.) I'm planning on neutering between 1 and 1.5years. Are there any issues concerns with that?
Later is usually better, and waiting until growth plates are fused is ideal. If you go through an ethical, reputable breeder they'll most likely discuss this further with you. Every vet I've talked to recently has said closer to 4 years seems like a good age, as there appears to be reduced risk of spay incontinence and the hormones are less necessary in a more mature bitch.
7.) most importantly, what is the amount of time needed for physical activity (not mental) per day? and please don't say 5hrs like one person tired to tell me, because unless your homeless or have no life, that's not happening.
Every dog is different. There is no guaranteed answer here. I have met dogs that didn't have an off switch, and I have met dogs that were happy to chill on the couch as long as they got some exercise and a bunch of training every day.