bitcoin is not profitable anymore. you should try altcoins. but if you will keep your bitcoins you can mine.
Bullsh**
For both BTC or altcoin mining only 2 things matter:
Cost of your electric
Being able to deal with the heat and noise produced
Cover those 2 things and you are Golden. The >US$8k/mo in gross revenue my 240THs farm makes is hardly chicken feed.
Is $0.09 per KWH workable? If so what mining hardware do you recommend?
Also do you know any good calculator (or how tos for a spreadsheet) to take into account changing difficulty over time?
0.09 is marginal for long-term mining. It's been viable since about Febuary this year due to a massive price jump on almost all cryptocoins, but profitability has been dropping a LOT the last couple months as the price rise leveled out and more and more rigs got online to raise the difficulty - and that trend will probably continue for a while since most of the BIG farms are in places with very cheap electric (under 5c/kwh and often more like 3).
Bitcoinwisdom calculator has a "diff increase percentage" field in the calculator, which is a lot better than the "nothing" most other calculators offer.