Welcome Snake eyes, and as has been said before, a very good summary by longshot. I know this is a very contentious issue, especially for newbies, my first rifle was gifted to me by a friend who imported it from the states, in two parts, without a UKARA, it arrived promptly and with no issues, apart from a rather hefty fee in import duty! It seems you've got that covered with the smaller packages and your experience with importing. I have imported some spare parts and upgrades and felt the sting of the import fees, It does make it seem less like a bargain.
I wonder how many prosecutions there are in this area? or how many confiscations for airsofters importing items? The recent theft of airsoft weapons in Essex is an interesting case in point, but without any context it is difficult to analyse. I would guess those were stolen as part of a "routine" burglary and the thieves would try to sell them on or possible use them for criminal purposes.
Are there any instances of airsofters either with or without a UKARA defence having "conversations" with the authorities? Is is a big problem? I would guess that most airsofters, understanding the sensitivities surrounding this are very sensible, always transporting the RIFs in appropriate cases and only using them at registered sites (or indoors at their own home?!).
If stopped and questioned by the police, what's the response/reaction you can expect?
If this is already a thread elsewhere, my apologies.
Good luck snake, let us all know how you get on!