[Elecraft] K3S Options - Install in what order to make it all easier?

[Chuck Milam, N9KY]

My apologies if this is a FAQ.  I've been looking all through the archives
and can't seem to find an answer, so I'm turning to the good folks of the
Elecraft reflector for some guidance.

I'm considering my first home HF station radio upgrade since 2000, and I'm
looking at the K3S.  The number of options are overwhelming at first, so
I've been reading and trying to narrow down what I'd need to get started.
I chase DX and do some contesting (all modes), so I'm thinking I'll get
some tighter filters, I know I'd like to be able to run an RX antenna for
low band work, possibly look at the sub-RX option as well for listening to
the other side of a split operation, etc.

Here's my main question:  If I'm building from kit, are there any
particular options I'd want to make sure I install first as to not make
things more difficult later?  For example, if I add filters now, then add
the sub-RX later, am I making things more difficult than if I added the
sub-RX first?  Would I be putting myself in the position of having to tear
the roof off the house to just upgrade the kitchen?  (Sorry, best analogy I
got at the moment.)

Thanks for your help and 73,

Chuck Milam, N9KY
N9KY at arrl.net