Well the only real lack of energy you get in Keto is during the keto flu, which doesn't even hit everyone. It happens in the first week or 2 of going low carb and most people get through it pretty easily with some powerade zero or chicken broth to replace electrolytes. Quite honestly once through that you'll have more energy then ever before! I know my energy levels shot through the roof after only about a week on keto.

Hello! This is normal. There's 3 basic stages of keto.

"Honeymoon: Lots of weight comes off fast. This is water that was tied up with glycogen. Note: if you don’t experience rapid weight loss in this period, do not despair. Not everyone is so lucky, and men may be more likely to see rapid initial weight loss than women.

Post-Induction Stall Syndrome (PISS): Water and glycogen find a new balance and this causes a stall or even weight gain, which lasts for a week or two. Relax, PISS is both normal and temporary.

Fully keto-adapted: After 3-4 weeks the body is burning fat as its main fuel and the brain has switched to running on ketones. A bumpy downward trend in your weight will begin. The trend is "bumpy" because there will be days or weeks when your weight stalls, or even goes up slightly. This happens to everyone, on every kind of weight-loss diet. Please don’t post to /r/keto that you gained a pound or two, or plateaued for a week. The trend will be especially bumpy if you are female. In particular, shark week will play hell with your scale weight."

(http://www.reddit.com/help/faqs/keto)

I would go all in at once. I did and lost 7 lbs the first week, and 3-5 lbs every week since. You can't cheat on it or you won't be in ketosis and won't see results.