In general i would say ;
Goggles - ideal for fast n furious proximity flying such as this
Screen - more use for camera platforms ( usually with baro , gps , mags ) where one would fly los then put the craft into a position hold mode and view screen / take pics .
I use fatshark Dom v2 , but hear good reports of those single screen headsets.
I also have a small screen (7")for image checking and adjustment on the bench and can transfer to 12" laptop via ezcap.
(Easy enough to get a vrx and make your own ground station. )
For £100 or so your choices are a good starting point.
AIO cam and vtx are also good enough .
Two sorts - cam and vtx actually one item - easy to connect - remarkably good quality for £15 odd (became v popular for tiny whoops. ) don't think you can change lens - EDIT - these also come with short antenna so poss no use on your robocat
- cam and vtx two separate items - still easy to connect ( sometimes direct of a 3s balance lead I think ) , good quality , £20 odd - allows upgrade to ccd type ( better quality for fpv) camera. -EDIT - so use this sort and a coax pigtail to antenna.
You might consider the £14 eachine switcher vtx and £35 swift 2 camera instead . Would get you top pic and volts osd.
If you are running esc with active braking then you absolutely must power your vtx gear through a stabilised voltage supply ( such as pdb output )