Most of the Airfix 1/600 ship kits are quite easy + straightforward to
build. However as many of them date back to the 1960s, the kit moulds
are quite worn resulting in large amounts of "flash", mould lines, sink
marks, etc. which can make assembly more difficult.
The Belfast is one of the better kits in the Airfix range, but it's
still recommended to carefully clean up the parts before assembly with
a small modelling knife. Sink marks (found in large solid parts like
turrets) can be filled in with modelling filler putty then sanded flat.
Another very useful tip (for any ship model) is to paint the deck +
superstructure before adding the armament and fittings (searchlights,
masts, lifeboats, etc.) This is particularly important if you're
painting a camouflage scheme! I found this out the hard way with my
first large ship model (1/350 Tirpitz).
The Airfix Belfast kit doesn't actually represent the ship in its
current preserved/museum ship condition, but in its original WW2
configuration (early/mid-war I think) hence you need to be careful when
using photos of the preserved ship as reference for painting/detailing
the kit.