You have made a good choice in terms of payload to mount rating weight.
The only downside is that the image scale for that combination is 3 arc sec per pixel which might not combine well with the large PE of these mounts that vary greatly from unit to unit. A range of 30-90 arc sec gets quoted.
This measurement was almost 90"
https://www.star-watcher.ch/equipmen...eriodic-error/
Phil Hart measured 50"
https://philhart.com/content/star-ad...f%20the%20worm.
I can't find an example but I remember reading some quoting 30".
Thirty arc seconds is a streak of 10 pixels if your exposure is anywhere around 5 mins or 1/2 of the worm period. A ninety arc second PE is 30 pixels of streak.
Are you going to autoguide or use lucky imaging? At 250mm, your lucky imaging subs might need to be very short.
Photos I have seen with the Redcat 51 look pretty sharp with some blue haloes around brighter stars.
See REDCAT 51 examples from Astrobin