Gaining Experience With Small MIG - Now Have More Questions

I just finished a project involving using my trusty Handler 120 for
modifying a trailer constructed of 3/16 inch angle (2 X 2 and 2 X 3).
With some last minute advice from Ernie and a few other great folks on
here, I got really satisfying results. Compared vertical up and
vertical down, tried overhead (ended up turning the trailer over to
cure that problem).
But success has bred curiousity. I've seen the recent threads and
searched back through the Group on the emergence of newer and better
dual shield wires and the debate over MIG for out of position work.
And I've got the itch to just do some experiments and practice on stuff
around 3/16 up to 1/4.
My first question involves multipass MIG for say 1/4 stock. I've
tested my machine on 1/4 before, butt joint V-ed out, Hobart HB28
(E70S-6), and C25 flowing 25cfh. I tried to join pieces with 2-3
passes and found that as I watched the puddle and tried to judge
penetration I would end up building the bead into a single pass weld.
Whether I traveled fast and did multi passes or went slow watching the
puddle/penetration and ended up with a single pass the results were as
expected - I could break the weld with repeated impacts due to
insufficient penetration. In fairness to that exercise I was using .030
wire and have since switched back to .024.
Is there some technique for running a multi pass with this size welder
that I'm missing? Based on the experience with every project so far, I
have gotten better penetration by traveling slowly to pump in heat and
get penetration - too slowly to avoid building up the weld all in one
pass. Should I set up the work pieces with a root gap? Leave a land of
1-2mm at the root of the bevel? I know the benefit of preheat from
reading and using in some projects, but I want to try some things out
for situations where the work can't be preheated easily.
Second question involves out of position MIG. Just for trying to
educate myself and build on my skills, would it be worth trying a roll
of E71T and practice some out of position? From what I've read, that
wire will still serve well for most of the general mild steel projects
I come up with.
Third question: Even though the Handler 120 lacks the ooomphhh for
.030-.035 wire when pushing the machine's upper limit, would it be a
foolish exercise to try out some .030 dual shield working in the
mid-range of the machine's ability? That's where much of my projects
fall and again I figure the wire wouldn't go to waste. I've also never
had a problem running .030 when working stuff less than about 1/8 inch.
TIA,
Mark J