I wrote a new post yesterday about my mexiletine dosing and it answers a lot of your questions. That post can be found here: MEXILETINE reduction.
I titrated up my initial mexiletine dosing by taking a single 150 mg pill daily the first week, then two 150mg pills daily the next week, followed by three 150mg pills daily thereafter. However, I found most benefit came from the single daily 150 mg dose. Improvement was immediate and dramatic from the single daily dose. Prior to mexiletine therapy I was flaring multiple times a day, every day. I experienced symptoms every 2-4 hours. That flaring cycle stopped 36 hours after the initial dose. I have experienced only a handful of minor flares per year since and those that do occur are both less painful and more easily mitigated. I do still have occasional paresthesia at night (pins and needles feeling) if I get too hot while sleeping under bedding. That can be eliminated simply by removing the covering.