Analysis is a very important factor in spell checking. Stemming and other techniques that change tokens is not recommended since it will result in giving stems as suggestions. Instead, you should use a very minimal tokenization/analysis process like the StandardAnalyzer or even the WhitespaceTokenizer plus a simple lower casing filter and a filter that removes apostrophes and the like. As with most things in search, there are always tradeoffs and you should evaluate the results in your application.
That being said, a common configuration for spell checking is:
Furthermore, on the field that will get this type, use
omitTermFreqAndPositions="true" to save a little space and time during indexing.
Use a <copyField> to divert your main text fields to the spell field and then configure your spell checker to use the "spell" field to derive the spelling index.