No, you cannot apply for a J1 visa while in the US. You must apply for a J1 visa from outside the country at a US embassy or consulate.
J1 visa and the bad credit
After your J1 visa expires, you can stay in the US for up to 30 days. It is important to leave the country before this grace period ends to avoid any legal issues.
You can look for another but if you do not get it by and renew before the time your visa expires you need to leave or will be illegal.
H4 visa holders are not allowed to legally work. H4 is a derivative of an H1 visa. H4 visa holders are allowed entry to US because they are dependents of H1 visa holder. H4 visa holders are not eligible for Social Security Number. H4 visa holder may apply EAD only if filed concurrently with the principal's (H1 Visa holder) I-140 petition OR if principal's I-140 petition is pending or approved. H4 visa holders are not allowed to work legally. H4 is a derivative of an H1 visa. H4 visa holders are allowed entry to US because they are dependents of H1 visa holder. H4 visa holders are not eligible for Social Security Number. H4 visa holder may apply EAD only if filed concurrently with the principal's (H1 Visa holder) I-140 petition OR if principal's I-140 petition is pending or approved.
Without any work experience you will not be able to find a legitimate company to sponsor you for an H1 visa so almost impossible. H1B visa has few requirements that includes bachelor degree, work experience. Sponsor employer should show to US department you are eligible for the work and you have required skill sets.
Difficult - the H4 holder would have to be needed and benefit the US economy in his/her own right.
No, any alien needs to have a visa depending on the purpose of visit to US. There are A TO Z categories of visas available based on the applicant's need. For example you should apply for K-2 visa for touring US, F-1 for student visa,H1-B visa for work visa etc.
They are very reliable as far getting a visa is concerned. The US visa consultants, for example, provide very helpful information on the application of visas.
You don't.
First you need to find a job. The employer needs to sponsor your visa. Usually the employers pay an immigration lawyer to take care of the process. If you are in US with other than student visa you will have to get your H1-B visa outside US. It usually coast the employer $3K to $5K. The lawyer has to show the USCIS that the company cannot find an American citizen for the following position. If you are a hi-tech skilled worker it should not be a problem. Every year around October the congress allocates limited number of H1-B visas. Most of these visas finished up around April/May. So if you apply after all the H1-b visas finished your case will have to wait in line for the next year.
you may need to provide a police clearance for the job, but not for the visa. I'm not sure what a "caution" is, but if it doesn't show up as a conviction on a police record, then there's no problem.