To activate single scattering everywhere, use command MULSOPT  with the
following values:

WHAT(1): 0.0
WHAT(2): 0.0
WHAT(3): 0.0
WHAT(4): 1.0
WHAT(5): 1.0
WHAT(6): > 1000.0
SDUM:    GLOBAL (GLOBEMF applies only to electrons and positrons, GLOBHAD
         only tho hadrons and muons)

Note that this choice is generally extremely demanding in CPU
time, except for particles of very low energy (a few keV), which
have a very short history anyway. In such cases, the single
scattering option is even recommended.

Yes, if you have activated recoil transport with EVENTYPE. In general,
however, they don't travel very far.

Yes, with the exception of low-energy neutron interactions. In those
interactions, energy is deposited by charged recoils. Some of them (protons
from scattering on hydrogen and from 14-N(n,p), alphas from 10-B(n,alpha),
light fragments from 6-Li(n,x)) are explicitly transported by FLUKA and
their energy is deposited by dE/dx. But in most cases, the recoil energy is
deposited via kerma factors averaged over all possible reactions for a given
energy group, so that energy is conserved on average but not necessarily in
a single interaction.
Note that "kerma" in principle refers only to charged particles and not to
gammas. But in the unlucky case of Germanium, and of some other elements
listed in Chap. 10 of the manual, gamma production is not available. In such
cases, the energy of the gamma(s) is added to the kerma, making the situation
even worse.
The reason for this is that the NJOY code, which is used to process the
evaluated data files (ENDF, JEF, JENDL...), calculates kerma as the result of
an energy-mass balance: and whatever energy cannot be accounted for is added
to the kerma. This is clearly a weakness of the system, intrinsically
related to the way the neutron cross section databases are built (in some 
cases one even gets negative values due to inconsistencies in the
evaluated neutron cross section databases).
No separate balance for each transition can be done due to the lack of
correlations in the original databases: only averaging over all transitions
make sense and produces exact, albeit uncorrelated, dose calculations (within 
the limit of the evaluated databases accuracy).

The question of K0's in FLUKA is very complicated. You can have "pure
states" and superpositions of states, hadronic and leptonic, short and
long: and some of these are relevant at production time but not at
transport time and vice-versa.
FLUKA considers in different ways neutral Kaons according to their origin:
If kaons0 are coming from the weak decay of some resonance, like for 
instance a phi particle, where the transport eigenstates matter,
then they are labelled KAONLONG (I.D.: 12) and KAONSHRT (I.D.: 19).
Otherwise, if they are coming directly from the hadronisation chain, or
from strong decays of resonances, they are labelled KAONZERO (I.D.: 24) 
and AKAONZER (I.D.: 25), according to their
parton content. These kaons, during particle transport, are then treated
as a proper combination of KAONLONG and KAONSHRT in order to have the
right decay properties.
From the point of view of hadronic interactions instead, only KAONZERO
and AKAONZER have meaning. Therefore, if a KAONLONG has to interact with
another hadron it is first decomposed in KAONZERO/AKAONZER

The transport of ions is off by default and has to be invoked by
the user with WHAT(3) of the EVENTYPE card. Note that this switches
on only ion *transport*. In order to simulate ion *interactions*
the event-generators DPMJET and RQMD have to be linked using the
script ldpm3qmd which is located in the flutil subdirectory.
Also keep in mind that no nuclear interactions are simulated below
100MeV/n in the present version.

No: FLUKA distinguishes between particles that are produced (COMMON block
PART) and particles that are transported (COMMON block PAPROP). 
All particles and resonances listed in Particle Data
Group, with the exception of those containing quarks heavier than charm, are
produced. Those which have a very short lifetime, i.e. the resonances with
hadronic decay, are decayed immediately after their production. The reason
is that even at the highest energies their path would be irrelevantly short.
In particular phi(1020) is indeed produced and has its decay list
according to measured branching ratios, in this case K+K- (49.2%) and
Klong Kshort (34%).
Internally to the code, produced particles and transported particles
have different numbering schemes. Only transported particle numbers
are normally accessible to the user.

Define a thin region with a material of low density in which you set
the transport thresholds for electrons and positrons to a value just
below beam energy (card EMFCUT). Electrons and positrons would then be
stopped in that region with the energy entirely deposited at the
stopping point. The region should be thin enough (and of low-density
material) such that other particles interact as little as possible
in it. Note, that the region cannot be vacuum. Electron transport
cutoffs are not allowed in vacuum since the energy deposition (at the
stopping point) would be unphysical.