From a VAST experience with RNA extraction/RT and correspondence with company R&D departments, I can say that unlike OD 260/280 (protein and phenol contamination; HAS to be over 1.8), OD 260/230 is pretty meaningless. It supposedly tells you about small molecule/salt/ethanol carry-over, but in reality I never had an inhibited RT reaction regardless of 260/230 - if your starting concentration is decent. Presumably, trace ethanol gets diluted enough and then evaporates during the incubation at 37-55oC (depending on reverse transcriptase). I find that with column-based purification methods adding a 1 minute spin without the lid prior to elution helps keep 260/230 more constant. With precipitation-based methods, after you remove the 70-80% ethanol wash, give the sample another pulse-spin and use a fine tip to remove all remaining ethanol before drying and resuspending in water.

As to concentration and quantity, ~200 ng/uL is a good concentration and your spectrophotometric readings are reliable in the range. I am not familiar with TakaRa kits, but all the ones I know make a recommendation in terms of quantity (500 ng sounds about right), not concentration (500 ng/ml as you quote). Bear in mind that you measure TOTAL RNA concentration, of which only 1-4% is mRNA (depending on cell type, differentiation etc).

Lastly, a critical parameter to your RT reaction is RNA integrity, not just purity. There is no need for expensive or fancy methods (like Bioanalyzer). If you can spare the material, simply run an aliquot (200-500 ng) on a small agarose gel as if it was a plasmid digest. Either TBE or TAE work fine. Ethidium Bromide and SYBR stain are fine. Don't run it for very long to avoid overheating and smearing - it is not an optimal type of gel for RNA, just a quick solution. Also, wash everything before use to remove RNase leftovers from DNA preps. You need to see three major bands: 28S, 18S and a small smeared band with tRNA/snRNA/etc. The top bands should be crisp and the 28S should be twice as bright as the 18S (also called 28S/18S ratio of 2).

Good luck!