Installing the aux fuel tank will give you about 308 Lbs extra fuel if I remember correctly, thats just over 30 min so it will satisfy your requirements of 3:30 fuel.
Your payload will only be around 170 Kgs on the first leg but on the 2nd leg after 1 hr flying you´ll have a 450kg payload!
Depends on your mission requirements.
Now I dont really know the B-230/B222SP but I thought it had the R-R Allison C-30 engiens, excellent engines but I have never heard of them bigger than 650 Hp !!!
The -750 engines in the U model have a 735 Hp 2.5 min limit. Is it really possible to pull more power out of the C-30 engine or is the Lycoming perhaps the more powerful option?
In terms of reliability there is absolutely no problem operating the Lycoming LTS 101, my company has 6 ea B222U models which fly thousands of hour every year for many years with no problems whatsoever, they are excellent engines after all SB´s and inspections have been complied with.
But expensive to operate, I´m sure the C-30 is cheaper to run.