That’s all there is, there isn’t any more is a catchphrase from cinema:  Ethel Barrymore’s most famous line in Sunday.

What will hold a lot will hold a little.  (What’ll hold a lot lot’ll  hold a little as it is often said.)
This expression is used when a container is far too big for the contents.  The reverse is You can’t fit a quart into a pint pot.  A quart is two pints.

A miss is as good as a mile means that if two things do not hit it is not important how far apart they were.  (I’m not sure I agree with the principle!)

That’s the limit!
This idiom is about someone having gone too far in their behaviour.

There’s room for a little one.
On a seat or in a car if everyone moves up a bit there may be room for a little one.

Keep a tally means keep count.  A tally was originally a piece of wood on which notches were made for the items of an account.  It was then split in two and each party given half.  It is possible to keep a tally of favours done for example.  (The Concise Oxford Dictionary)  If someone says I’ll repay you after a kindness, the helper might say, “I’m not keeping a tally.”

It doesn’t tally means that something does not agree.  Again it could be accounts or someone’s behaviour not living up to their words.

Boundless is without limit.  Young animals seem to have boundless energy.

Testing the boundaries is what children and teenagers do to see what behaviour they can get away with.

A tidy sum is a large amount of money.

A fair amount is quite a lot.

Get more than you bargained for is a phrase used about the possible consequences of actions.

All things in moderation is an expression about not eating or drinking to excess.  Nowadays in moderation has taken on a new meaning with comment moderation and moderators of computer forums.

A tall order is a request which is almost or actually impossible to fulfil.

A cushy number is a job which does not require much effort and is well-paid.

Half a loaf is better than no bread is a saying.

The narrow way is where Jesus’ followers have to enter.  Matthew 7:13-14

The widow’s mite was all she had to live on, yet she gave it as an offering in the temple.  A mite was a small amount of money – a fraction of a penny. Mark 12:41-44

Mites are also tiny arachnids, eg red spider mites, and a small child might be referred to as a little mite.