It depends on several factors.
First, the amount of meth: Possession of meth for resale is a B felony (8-12 years as a Range I offender) if the amount is 0.5 grams or more of meth but a C felony (3-6 years) if the amount is less than 0.5 grams.
Second, his criminal record: Is he a Range I offender, or does he have a criminal record that makes him a higher category?
Third, the prosecutor and the strength of the case: What will the prosecutor offer him a plea to? He/she may not ask him to plead to the most serious charge for a variety of reasons. Relatedly, how strong is the case for intent to distribute? If it's not strong, he may be looking at much reduced exposure.
Fourth, the court: If he goes to trial and loses, what might the judge sentence him to? Straight time to serve? Split confinement? Straight probation?
These are some of the main questions to be answered, but they're not all of the questions. It's crucial for him to get good legal representation to get the proper questions answered with a goal of minimizing his exposure.
It's impossible to say how strong your case for suppressing the evidence is without seeing the search warrant itself, but your lawyer should have that and so should be able to say.
Generally, the validity of a search warrant hinges on whether the affidavit in support of it establishes probable cause for the search by looking at the totality of the circumstances as laid out in the affidavit. So, if the CI's word is the only information in the affidavit, the failure to satisfy the "Gates test" (which incorporates the two prongs of the "Aguilar-Spinelli test"--the two-pronged test I assume you're referring to--but which stresses that they are not the end of the inquiry) may well result in suppression of the fruits of the search. On the other hand, if there's more in the warrant affidavit than just the informant's tip, then the (maybe unspecific) word of a (maybe unreliable) informant is less important to the overall determination of probable cause. It's also not a winning argument to say that the informant's tip isn't specific enough or that the informant isn't reliable enough and so the tip itself is effectively erased from the affidavit; the magistrate can still consider the tip as part of the totality of the circumstances, even though it would not have been a valid basis for the search warrant all by itself under the Aguilar-Spinelli test.
As a practical matter, if the CI did a controlled buy from your house, there's probably going to be more than just a tip in the warrant affidavit, and so it's a bit unlikely that the warrant will be suppressed. But--I stress again--your lawyer will be in the best position to evaluate the chances of suppression by attacking the search warrant, because he/she can see what's in the affidavit.