Just got a new used r53 love it. Wondering how much H.P. is ok for the aisin 6 spd any thoughts

 

Welcome!!
Pretty much as much as you can make. The r53 stick is not a weakpoint that will cause you any issues till you make crazy (nonstreet) hp.

 

Sorry I meant 6 spd auto, any limitations on HP

 

Biggest factor on the auto is finding a tuner to custom tune the ecu. It is harder, but can be done. Still, the failures of the asin auto tranny have not been hp related.
thr mini's ecu handles mods pretty well, so a custom tune is not needed till many changes are made, and then it is mostly to optimize effecency, and to get a few more hp.
folks typically run 220 hp give or take a few on most daily driver modded mini's...more basic mods less, more agressive a few more, but that is the range...and about the lumit when it comes to using the hp in a light fwd car...more is just to brag.
The auto tranny is not perfect, and can have issues (mini's tend to be agressivly driven...go figure), but a few folks have found a vave body tweak used in the same tranny that seems to fix things used by vw and audifolls...same tranny.

 

PS
It is MUCH more common to have other, non tranny failures before the tranny....but starting with a used car....as they age, the weak links change...things do age, wear....