There are much more cost implications to this suggestion than you first think.

Although it may reduce initial premiums, it will not help with all other insurances you will need to get. Also, you imply you are enthusiastic about all types of cars - some even at group 20. Generally this can be more expensive than insuring singularly, although it is simplifyed a great deal.

Perhaps try giving a broker a call on this one; I'm sure they'd give you some sort of advice. Tell them you have already got lots of vehicles otherwise they will lose interest and 'bore you off' to Call Connection! (a useless transfer agency)