Politely decline those with poor credit or insufficient income.

The problem with the Tax Sales is lack of notice or insufficient notice. 

If after appropriate investigation, it appears to such officer that the proceeds from the sale of the property would be insufficient to wholly or partly satisfy the lien of the United States, or that the claim of the United States has been satisfied or by lapse of time or otherwise has become unenforceable, such officer may issue a certificate releasing the property from such lien"Locate the "officer charged with the administration of the laws in respect of which the lien of the United States arises" from the lien (a sample is provided here for the property I was researching - Assistant US Attorney Erin Secord) and contact him/her in advance to find out what information they would require from you if you win the bid.

Not to mention, the boyfriend will not qualify as a tenant due to criminal record, insufficient proof income and several other requirements.

Moreover, the value of the land is low compared to the construction cost so the land would be insufficient anyway and the distressed value would be very low because who would be interested in paying up for land with something partially built on it.

This is insufficient for the insurance company and the seller has been unresponsive when my attorney has contacted his attorney for the full billing statements. 

From my research, this budget appears to be insufficient for acquiring most MHPs currently on the market.

If you feel the income would be insufficient and put you in jeopardy of receiving your rent then find someone with more income.

I foresee us being stopped dead in our tracks due to mutual insufficient credit scores in the near-future and the inability to perform a cash out.Any input would be much appreciated.

Considering that you indicated having insufficient funds for extensive rehabilitation, it may be easier to discover a home that just need minor cosmetic repair.Before completing the transaction, thoroughly check the property.