no problemdue to the lenght, a forum lives from posts ;)
everybody reacts different of a certain workoute routine, so if you really want to find YOUR ideal split, you gotta try things. if you are successful with a certain routine just stick to it as long a you donßt continue processing. so your aswers:

1. just exerience, some guys get around with once a week others with twice. no matter which one, you always have to give your best. if you´re on once then you do more sets then on twice, but no matter which one: always get the most out of it. as youe´ve already said: if you feel better on twicw then just do it

2. your routine(the one you posted) was not that bad, but could be better. legs do not fit with tris. first you got all your blood in your lower body and the pumping it up in your tris ? on a 3 day split you should do legs alone without any other muscles, exept abs and calfs.
for the other 2 days you could do:
1: chest, shoulder, tris/or bis
2:back, bis/or tris
or
1: chest, back
2: shoulder, tris, bis
or
1:chest, tris, bis
2: back, shoulder
or
1:chest, bis/or tris
2:back, schoulder, tris/or bis
but i would recommend you the -chest, shoulder, tri-s and -back, bis- version. you´re also doing to much for arms. just look; your doing equally as much for bis as for chest, thats way too much.
stick to: 9-12 sets for chest, 9-12 for back, 6-9 for shoulders, 3-6 for bis and tris, 12-15 for legs (calf, abs: 3-6, you can train them more often )

3. the aba bab sounds not bad for me. if your doing a 3day split you can train every second day. with a 3day split you can also train every muscle roup every5 days. it would look like this:
mo: chest, shoulders, tris
tu: legs, abs
we: off
thu: back, bis, abs
fr: off
sa: chest, shoulders, tris
su: legs(no abs today, twice a week´s enough)
mo: off
tu: back, abs
we: off
thu: chest, shoulders, tris
fr: legs, abs
sa: off
su: back, bis(no abs, twice a week´s enough)
.....
just decide which one suits you best