How much exercise for my dogs?

I have a small/medium size mutt... and we don't really go on walks. She has never been taught to walk on a lead, only to go potty while on it. I COULD teach her to heel, but, I am overwhelmed trying to teach her several other things. She is about 6 months old. We spend several sessions a day playing fetch, and I throw her toy far enough for her to run back and forth, and we stop when she loses interest. Sometimes if she gets wound, she runs maniacally around the living room for about 1 minute, and I let her do that as long as she doesn't get on the furniture or do anything else she's not permitted. I mean... how MUCH exercise is enough? Should I be doing more? She doesn't care for the outdoors (even though she's a beagle mix).

She is not at ALL fat. She's actually borderline thin. She eats plenty, and she has a vet appt soon. She just gets very hyper and jumps on company, so I'm curious if her exercise is sufficient. She sits, lays down, shakes, has a good recall, crawls, speaks, gives kisses, and several other tricks/obedience practices on cue. I am focusing strongly on getting her to STOP jumping on people... but we are having bad luck with that. I just wanted to know if wearing her out more would help.

Sounds like you are doing great :o}
As long as her weight is good and not fat at all she'll make up her own exercise as she goes with ball playing etc with you.
a tip though,,try and teach one or 2 behaviors at a time,, because if you are getting overwhelmed at so much training, she probably is too.
Choose whats most important first,,usually come and sit are good starters,after that lay{down} stay and such.

How weird!
A beagle not caring for outdoors? :O
Well, you sound pretty active.
So you are doing fine. :D

Yes, you should. A dog's natural instinct is to walk - not go back and forth in the same spot, but walk. You say you're overwhelmed teaching her several other things, but teaching her to walk on a lead is the most important one you should be doing her age. By the way, she doesn't have to know how to heal, only to walk close enough to your side that she's not pulling you along and that's not at all hard to teach. If she doesn't seem to care for the outdoors, are you sure that's really her or is she just not socialized because you don't try.

Dogs exercise all day when they are free to roam;However, Hound Dogs should be kept locked up till ready to run because they love it so much they run themselves to death.

I would recommend High Protein Dog food for your Dog if your gonna exercise him allot.

My Aussie will be 2 years old this weekend.

I regret not teaching "Heel" because when we
go for walks, he is walking me(pulling, stopping,
sniffing, barking).

He is a great dog, but has a few unwanted behaviors,
including the walking issue, and jumping up on people etc.
I got the book by Cesar Millan -the Dog Whisperer. After
reading it, I am sold. Explains alot why dogs do what they
do, and much of it is due to well intended owners not
doing their share.
According to him the MOST IMPORTANT
thing you can do for your dog is WALK HIM/her at least
an hour a day (as a puppy im sure you can reduce the time.
Walking not only exercises the dogs body, but helps
establish YOU as the leader- a role you must maintain
24/7.
I have seen improvement in my dog, but we still have lots
of work, but at your pups age, I would definitely include
"heel" and walking on a leash as part of daily training, even
if it means you put one of your other commands on the
back burner for a time.
Good Luck