Visa expires in April. TPS application pending. Am i allowed to stay until i receive decision on my TPS Application ?

If this is a renwal you are good until July. However, if you are a first time applicant, you may be out of status after your visa expires (even if application is pending).

If you are on an h1b, you have two months of "grace period" after visa expires so you would be good until June.

You are allowed to stay while your application is pending.

Am i allowed to work as well as stay after july if my TPS application is still pending?

When your application for any visa or status is pending, say you applied when you were IN STATUS, you will be considered to be here legally if your TPS is eventually approved. However, if your TPS gets denied in the end, I believe the time you spent after your old visa expired will count as out of status time. This is my understanding from what I've heard. Please consult an immigration attorney for accurate advice.

A request to change or extend status is only considered properly filed if it is submitted while the individual is still in a valid nonimmigrant status. As explained above, this generally means that the person holds an unexpired I-94 and is complying with the requirements of the status indicated on that form. In most situations, if the individual’s status subsequently expires while the request to change or extend status is pending, the foreign national falls out of nonimmigrant status, but remains in a period of authorized stay. This period of authorized stay continues until the USCIS issues a decision on the pending case. If the application or petition is approved with an extension or change of status, the decision has a retroactive effect, meaning that the period without status is cured.