While getting there is a great goal, probably not a realistic place to start. I think 500 would be more reasonable, and that may be a bit much. Like everyone that comes on here asking for advice you either have been or will be told you need to find a good team-vet, someone to help with marketing, nutritionist, "evil" banker, part time labor, an understanding wife is probably going to be the most important.
5,000 head is a whale of a place to start, or even end up after several years (decades). You're looking at $3.5 million in just purchase price on the cattle, nevermind facilities, feed, labor, etc. I know that you've said that you understand that, but finding someone to bankroll that is a going to be tough.
My customer that backrounds figures that if he can't show at least a $50/head profit on them before he buys them then he doesn't even try. There is almost always going to be something that pops up that knocks that number down (death loss, extra drugs...), but then a lot of times something works with him and that gets bumped up (lower feed cost, better conversion...). He is growing his own feed, has equipment and has 30+ years of experience doing it.
One last thought in closing, there is a point in every operation and business where one guy just can't do it all himself. Then you start have to hiring help, I think that everyone that has managed people will tell you they would rather manage a monkey poop fight at the zoo most days if given a choice. Did they show up, do they have to leave early, did they have a fight with their husband/wife last night, is their kid sick, and on and on. Depending on how you set it up you might be better off dollar wise and more sane with 2000 head than 5000.
