instrument flight safety is dependent on your skill set and currency. That said flying in smooth conditions with minimum maneuvering is relatively simple, I find it easier than VFR especially if relying on radar guidance. Flying IMC with no Radar cover is in my opinion foolhardy as you have no way of knowing whats out there.
Coping with heavy turbulence is another thing. you will be working very hard to control the aircraft and single pilot IFR is hard work even having another pair of hands to cope with radio and setting up NAV is helpful and reduces the workload.
Minimum instruments required depends on whether you want legal IFR minimum or added safety.
Really for flight in the UK with IRR your limited to non airways and without de-ice your stuck with above freezing levels .
There has been a nasty reduction in the number of VORs in the UK recently which means getting a VOR approach is virtually impossible so you are limited to ILS NDB or a small number of Radar surveillance approaches. To be legal you need NAV boxes that are FM immune which most of the old kit does not have, though for training you can get away with it.
I did my initial IR training in a basic trainer in cloud not simulated which looking back was very good training tho at the time was scary! The visual minimum for take off landing is 1800 m which means with high power runway lighting pretty poor vis. Actually, anything below VMC minimum require instrument qualifications so the answer to your question is yes 1800m is below VFR so thats IMC conditions - but its not the same as en route in cloud vis which is pretty much 0m.
When I did my IR training it seemed scary at first but you get confidence with time and really the key is very gentle inputs and correct trim. Its well worth doing an IRR just for the added ability you gain even if you don't want to plan IFR trips. Also remember non IMC trained pilots last a very short time in IMC so having the skills is a good idea.