On 160m even with the smaller output from the cardioid loop the Loop Antenna Amplifier + will have enough gain. You could try increasing the loop size to 2m but you would loose performance at higher frequencies.
It would be a waste to use copper pipe for the cardioid loop, with the resistor wire works fine.
With a phasing unit if two loops are facing in the same direction (towards the USA in your case) they don't need to be inline or broadside as you can adjust the phasing between them for maximum gain. If they are not inline or broadside it may give a skewed pattern of nulls but this may be an advantage as you will be able to steer the nulls with the phasing unit at the expense of a dB or so of forward gain.
The original C and S Antennas cardioid loop array used four cardioid loops to give a very sharp forward pattern using separate coax phasing harnesses for inline or broadside operation.
I made a prototype phasing unit about two years ago and it was excellent at phasing two antennas especially nulling out noise or interference. We decided not to go ahead with it as it needed a lot of workshop assembly. I did get a lot of practice and experience of phasing antennas with it.