Lathe Indexing Tools

[m_c]

For smaller lathes, you can't really go wrong with CC_T insert holders, as the insert choice and cutting angles are a good compromise. The insert size is upto you, however if you're getting a boring bar, it's worth going for the smaller inserts, as it reduces the number of insert sizes/types you need to have.
A SCLCR holder is what you'll most likely be looking for, as it's the most versatile in terms of turning/facing.

I've personally never bothered with triangular inserts other than for threading, as they're not as versatile, and in 12mm shank sizes you're limited to size 11 inserts, which aren't as common.

Have a look at http://www.shop-apt.co.uk/lathe-turning-tools-apt.html as it shows the directions that the tools/inserts are designed to be used. You can use them in other directions, but it's not recommended.
(and if you're looking for insert parting tools, look at the grooving section, as APT's grooving/multi direction WDN insert tools are pretty good)