What is the future of a cryptocurrency developer?

I am a Nonresident Alien and I live in Ensenada Baja California Mexico. I’m about to buy many electronics. Total value would be around $12,000 for my personal use. I am building my own house and I want to buy from SEARS in Chula Vista, California, but I don’t want to pay double tax (in the US and Mexico) since I am going to import the merchandise to Mexico. Is there any way to avoid the payment of taxes in Chula Vista?

Is a credit card statement considered a viable replacement of a receipt for income tax documentation of expenses or are credit card slips still required?

I am doing freelancing for two different companies and I have several questions. I deliver for them digital files, such as research, PowerPoints or excel files. Do I need to add sales tax to the invoices? When and how do I file taxes? I have never worked before in California and just started working in October last year.

If I participate in my employer's 401K plan, can I also set up a SEP-IRA for my self-employment income?

What is the best way to save credit card surcharges?

What are the tax changes I need to know about when filing my individual return for 2012?

When can I file my 2017 tax returns?