Hello and Welcome,
Thanks for fostering the mama and kitties! His avatar is adorable!!!!

He will learn to maneuver with his 3 legs have no doubt cats do amazingly well on three legs!

Purrkins is a left front leg amputee he was 6 at the time of his amp so I have no experience to share on kittens.

– I’ve read on some other web sites that it might be better to amputate the entire leg instead of having the animal keep trying to walk on a partial leg. When he is trying to walk, he is trying to use the leg with the non-existent paw, so he ends up essentially crawling on the stump. I asked the foster coordinator if he should see a vet and she said there is nothing that can be done about it, and he will just have to learn to live with it. I’m not sure I like this answer. Should I insist that he see the vet, or take him to one myself? And if they did decide it would be better to amputate the rest of the limb, what age would they do it at? Right away, or wait until he is a little older? I’m not even sure if a kitten at three weeks could handle surgery.

Your instinct is correct on not liking that answer! There is something that can be done. Unless someone can provide the care and cost needed for a prosthesis the entire leg should go it will end up causing problems for the kitty he will try to use the stump! It would be easier on him without the stump. Purrkins scapula and entire arm were taken he had cancer on his wrist. That is what most front leg amputees have done.

When? A Vet would have to tell you when is best on the timeframe? 

- Any suggestions for a litter pan that he can get in and out of easily? Even a kitten sized litter pan would be way to difficult for him to get in and out of at this stage. I'm wondering if maybe one of those disposable aluminum cake or pie pans might work. 

We have a forum Litter Box Tips for Tripawds – Member Tips  litter box ideas and what we have all done to help our trikitties.

Sure an aluminum pan would work. If it were me I would cut out one side for him to get into it easier & make sure there are no jagged or sharp edges. A disposable litter pan cut out would also be an option.

As you will see in the litter box forum, we cut our litter box out for Purrkins.

- For those of you with a cat missing a front leg, are they able to climb, and if so are they able to jump down on something without landing on their head? I'm not sure if I should limit what he can access in his room right now or not. Obviously the rest of his siblings are getting ready to run and climb and play and I always give my foster kittens a scratching post or cat tree to climb and play on, but I don't want this little guy to get hurt jumping down from something.

YES, Purrkins can do all things a kitty on four can do on three! Purrkins had a relearning process since he was six at the time of his amp, your kitty will figure this all out quickly! Treat the kitty the same he will need a scratching post & my advice would be to protect that remaining front leg by providing steps. We have one leg taking all the load instead of 2providing easier access for ups and downs by any means you can. Purrkins took to using his steps right away. You can train the kitty to use the steps too with treats.
Remember, Safety First with DIY Ramps for Cats and Dogs 

Anything I else I need to consider based on your experiences?

Kitties on three legs need fewer calories. I'm not sure on your wee little kitty, but eventually, he will need fewer calories to keep his weight down. There is loads of information on the site take some time and read the forums and blogs.  I know all your concerns will be less seeing what a trikitty can do not what they cannot do;) You can read about Purrkins journey on Purrkins blog.

Let us know if you have other questions and how things go from here.

Hugs 

Holly & Purrkins