Thanks for useful info, I have RPi zero but without wireless and BT, using it in another project for now 
Also found that power limit of AXP209 chip can be “unlocked” with command axp209 --no-limit or i2cset -y -f 0x34 0x30 0x63 so it can use more than limited 500mA. Not good idea to plugging it on computer, USB port cannot deliver that much power but if used with adapter 1,5 A or more it will be ok. There is even a script for this (github.com/fordsfords/axp209-no … e/gh-pages)
I googled for CPU monitoring and found **htop **that is ok, I was thinking of some logging tool that I can use to see in past if there was high CPU demands, but this is ok for now.
Currently dump1090 is using about ~35% and other processes occasionally take additional ~5% so in total average around ~40%.
Next i will experiment with some LNA, homemade filter and antennas. I found so much useful info on this forum but not too much spare time 