As Max says a split will 99% of the time give a significant uplift on the total.
When I buy outfits I would expect to be "given" every extra as in many cases they would just duplicate items I have or not suit my use.
Normally I would say the same of a trailer as I'm always looking at outfits with 15hp maximum and carry in the car so the trailer is just a nuisance I have to sell on.
If your outfit had a rougher trailer and a 15hp I'd say this time of year £1200-£1500 is what I'd want to pay. But yours all looks exceptional and with a 30hp hard to value as it would be too large for many and put them off... often a 30hp will sell well under the price of a 15hp... but get the one chap like Gurnard for example who wants exactly that sort of outfit and it actually may fetch strong money as an outfit.
Here is a completed sale that may give an idea of outfit prices...
RIB ZODIAC - INFLATABLE BOAT- OUTBOARD YAMAHA 30HP | eBay
Similar outboard, rougher trailer and swings/roundabouts on a far more expensive when new but now older boat.
If I had to go for a gut feeling with the items split...
30hp - £700
SIB - £600
Trailer - £300
Extras - £100ish
In truth though it's not a great time of year but if storage is an issue I reckon the peak selling period isn't until May so it's a fair time to wait for best price.
For me Ebay is still the biggest marketplace... it sold my £1500 outfit easily a couple of months back.... of course it's free to try here first.