APM2.5 with newer RTK GPS

Hi All,
Hoping to get some answers here as I’ve searched and searched but there’s just too much to read through.

I have the Ardupilot 2.5 hardware.
I am building a rover with differential or skid steering.
I will start with remote control but intend to convert to autopilot when funds allow.
I was thinking of using the Here3 with NTRIP RTK updates from a local government run station.

Will the old autopilot support the newer gps/rtk reciever?
Will it support rtk ? will it support here3 gps?

Also, I saw someone had installed 3 compasses and 2 gps’s to a rover before.
What other methods could I use to get <20cm accuracy ? Is it easy enough to wire extra gps’s or compasses?

Thanks in advance for your replies.

No, it does not support RTK. You need newer hardware.
And no, APM 2.8 won’t work either.

yes, all is possible with newer hardware.

Thanks for your prompt reply. Confirmed what I suspected.