How doI get back my security deposit, plus related costs,if the condition of the rental was worse than what was represented?

If the landlord does not return your $400, you could sue her for that amount plus the cost of your supplies and your labor in working on the place.  If there wasn't any agreement as to your hourly rate or other rate of compensation, you could recover the reasonable value of your labor based on the market rate for such work in your community.

Although you only had a verbal agreement, you could still sue the landlord for breach of contract because you paid $400 due to detrimentally relying on the landlord's representations as to the condition of the premises.  Detrimental reliance means that you would not have entered into the agreement, paid the $400, purchased the supplies and worked on the place had you known about the faulty electrical wiring, mold, water leak, etc.

Your lawsuit against the landlord for breach of contract should also include an additional cause of action (claim) for misrepresentation since the landlord did not disclose the dangerous conditions on the premises such as the faulty electrical wiring, mold, water leak, etc.  Misrepresentation is intentional misstatement or omission or nondisclosure of a material fact to induce your reliance causing you damage.  Here, the landlord did not disclose the dangerous conditions in order to induce you to pay $400 and make all repairs.

Your photos of the condition of the premises including photos of the mold, water leak,  and a statement under penalty of perjury from the electrician regarding the faulty wiring being a fire hazard will provide you with additional evidence in support of your claim.  This evidence is important because the problem with verbal agreements is that it becomes your word against the landlord's.

Damages (the amount you  are seeking in your lawsuit) should include the $400 deposit, cost of your supplies and labor as mentioned above.  You should also include court costs such as the court filing fee and process server fee.  You may be able to file your lawsuit in Small Claims Court.

If you had entered into a lease, you could have terminated the lease and sued the landlord for breach of the implied warranty of habitability.  The implied warranty of habitability is a part of every lease and requires that the condition of the premises be habitable by conforming to local or state housing codes.  The dangerous conditions on the premises (mold, faulty electrical wiring, water leak, etc.) would  breach the implied warranty of habitability.