Typically you use 5C to hold smaller stock that doesn't hold well in 3J chucks or 4J. I use the 5C about 50% of the time for small diameter work. The larger collet system for larger stock, a collet system like 5C and 16C is less than ideal because it only holds stock at the tip of the collet. You get more skew and run-out with these types of collets. If you want to hold bigger stock then use a 3J or 4J, if tubing then a 6J chuck. I would not waste your money on very expensive collet systems need to hold stock over 1". The only "inexpensive" collet system is an ER-40 set collet chuck sold by Shar's and you need to turn a back plate. The down side with ER systems is it does not do a good job of holding very short stock, it is cumbersome (at least for me) to wrench the collet nut. You need a 1/32" increment collet set to effectively cover clamping all size stock, the largest collet is around 1-3/16".
Not to down play this size lathe, but I would give some consideration to what you will be using the lathe for and different options given the power requirements and additional expenses for say adding a 15 HP RPC. A 1440GT will have the same size spindle with a shorter headstock, and most the features you describe. A 3 Hp VFD will run around $320 and you are good to go, other than the tooling. Buying a 15 Hp RPC panels and wiring will add up quickly. I have yet to have anybody complain that the 3 Hp stock 3 phase motor was a limiting factor. A bigger lathe is nice for rigidity, DOC and work envelope, but everything is bigger and costs more.