The basic idea behind an L1 visa is to allow employees of international companies that operate both inside and outside of the US to be transferred from an international branch to the US branch. I’ll try to answer each of your questions here.
First, the employer will file an L1 application on your behalf and each individual application will be evaluated by USCIS. So, how easy it is to get will depend on your qualifications. In some situations and for certain employers, USCIS will issue blanket L1 visas, meaning they issue a certain number of blank visas and the company then distributes them to employees on their own in which case it would be a lot easier for you to get.
The time restriction on an L1 visa generally range from about 3 months to the max stay of 7 years. The length of issuance is based on reciprocity considerations with other nations so your visa will be issued for the amount of time specifically set out for your home country. The good news, though, is that there are no quota restrictions on an L1 visa like on an H1B.
Any visa application process is going to take some time and effort, the L1 is no different. There are a lot of forms and paperwork that need to be filed between 6 months and 45 days before the employee’s requested start date. But, before that can happen, all of the required information needs to be gathered and the forms and paperwork need to be actually filled out. This process can take a few months on your own, but hiring an immigration attorney to help you can make it a little easier and cut down on some time.
Finally, your last question, can you convert to an H1B once in the US? It is possible to convert to a H1B visa, but the application process is independent so you would have to go through the process again to get your L1 converted to an H1B.
Like I briefly mentioned, the process becomes easier with the help of an immigration attorney. An experienced immigration attorney will be familiar with the process so they will be able to work with you through your process to make sure that you can meet all the requirements.