The instructions for Form W-4 include a worksheet to adjust your allowances based on deductions and adjustments at the top of page 2. This worksheet is based on estimates so there's no set maximum number of allowances, but you should use reasonable estimates on the worksheet to calculate the proper number of allowances. If you claim too many allowances and end up owing more than $1,000 then you are subject to interest and penalties for underpayment.
That said, I don't believe a 2018 W-4 is finalized yet, I only see a draft version. Depending on how you are affected by the new tax law, you may not need to make adjustments to withholding. You could either wait until next year to adjust allowances based on the outcome of your 2018 return, wait until the 2018 W-4 is finalized and adjust then, or take a best-guess now and keep an eye on it over the course of the year.
The misdemeanor charges referenced in the other answer would be in extreme cases where you choose a number wholly unsupported by reasonable (good-faith) estimates (ie the worksheet suggest 5 allowances and you choose 15) with the intent of avoiding taxes. Criminal charges are not an issue if you make reasonable estimates and are off by a bit.