Im blundering my way through my first pd patch and im having a bit of a problem implementing something....

I want to have a bank of 4 loop recorders which record for 16 `beats` (a beat being a counter controlled by a metro cycling from 0 - 15)

Basically I`m wondering whats the best way to store the information? I want to be able to go between 60 and 250 bpm. Is it easiet to just have an array which stores up to 12 seconds audio (for 60 bpm) and just adjust the length which is read by a tabread~ object?

Pd files doesn't store very well informations, you might loose data contained into array after an certain amount (relatively high) when you save, close, and open a patch (but maybe that's not what you would like to do?), storing sound into a raw or wav file with sfwrite~ before closing the patch might be a good solution.
Below something like ten seconds, my looprecorder even use sfwrite~ (so it's writing directly on hardrive) I haven't got a significant latency (maybe because my harddrive is 16Mo cache ?)

Also you might encounter a click problem between the starting point and the end point.
There are many solutions for solving this problem,
using an adsr, or trapezoid in cyclone librarie, or modifying the last levels inside the array for adapting it to the begining of the data in the array with a magical patch...

For resolving this click problem with the looping point, using an array is certainly the best solution.

so a set length array slightly longer than the longest length the loop could be (eg 32 seconds for 2 bars at 60 bpm) which i can quickly fade at both ends is the best bet?

I've made some time ago a looprecorder with Thomas Grill xsample, if you want to try it's attached.

Turn the clock on, move the step number value and play into your adc~
like you see in the exemple you can access to every parameters with send and receive.

http://www.pdpatchrepo.info/hurleur/looprec.zip