Once the tax lien has been withdrawn it will be removed from your credit report and if you have no other public records you should see a significant increase to your credit scores. If there are other public records (judgment or bankruptcy) then your score will still be impaired, as having any public record is damaging and only getting rid of one public record when there are many will only result in a minimal score increase.
As far as your child support arrears are concerned, most lenders will require the past due arrears to be paid in full, and the title company may also as well (as they will do a search for past due child support) even if the lender doesn't require it. In the situation where the arrears have been on a payment plan for 12 months then lenders will start allowing them to remain past due, but will count the payment on the arrears in your debt to income ratio along with the normal child support payment. Also, if past due child support is reported on your credit that also often damages your credit, so becoming current on that may be another way to increase your scores.
Your credit score isn't really the problem, it's the lien and chid support that under writing may have a problem with. 12 months paid on time is a plus but I agree with some of the others in this forum, the IRS doesn't remove anything unless paid in full. I have refer you to a VA lender I know that can look at your situation and advise. Just let me know through my profile and I can send you her information.
I have never seen a tax lien removed from a credit report in the 25 years I have been in mortgages. Do you have a payment schedule with the IRS? If so you will need a copy of that and proof that you are paying them per agreement.
When was your child support arrears? If within the last 2 years it is still counted against you in the credit score and underwriting.
Please email me at : theJORYgroup@gmail.com...I can forward you the information to get approved. There are VA loans available with mid ficos @ 580. We also have some other tools we use to make it happen for you.