Min/max height of B-tree
In the worst case you will store 1 record per node, so you will need 1000 nodes.

In the best case you will store 4 record per node, so you only need 1000/4 = 250 nodes.

In the worst case you will have 3 children per node, so your tree will only grow by multiples of 3 for each level.  So we can say that $3^h \geq 1000$, where $h$ is the height.  So $h=\lceil\log_3 1000\rceil=7$

In the best case you will have 5 children per node, so your tree will be $h=\lceil\log_5 250\rceil=4$