My best tool is the IRS website and to some degree publications.  I do have access to get unique information from my professional associations (I am a member of three) Regular internet is great too but the information is not always correct..

Most of my clients like email, mostly for practical reasons as I must have copies of all documents in case the IRS asks for more information.

I do have a secure portal to send and receive information that is approved by the IRS as by law no data can be saved on a server outside the US.

This season I will also invest in electronic signature opportunities and to also that you can use your mobile phone  to upload documents and the information goes straight to the tax portal.

I also make sure that I mainly work remotely and as an Enrolled Agent I can do taxes for any state, something that a CPA cannot do.

I can also represent clients before the IRS with a Power of Attorney legally in any state too, it is just a matter of if it is via letter or office  audit. Some states do have their own rules but most only require that you have sent in a special application to the IRS.

I have my "Rolodex" with people I am working together with regularly, like tax lawyers and CPAs/Accountants.  Other are specialists in special areas like my PowerCore team and others.