EURL - Startup obligations, TVA

I am a U.S. citizen living in France.  I have been living here for about one and a half years.  My Titre de Séjour indicates that it is valid for ‘Toutes Activités Professionelles’.

I have just created an EURL (in November, with a capitalization of 1000€), including having received my SIREN/SIRET and (apparently) my TVA number.  The EURL has so far had no income and has submitted no invoices, and has incurred about 3000€ in expenses (which have been paid personally).  At this time, I expect to have only the one client with whom I am currently working.

Questions:
1 - I have the impression that my first end-of-year accounting will occur at the end of the first full year of operation.  Is this correct?
2 - What are my obligations in the mean time?  I know that I need to maintain records such as invoices sent, and expenses incurred.  What submissions will I need to make?

My current activity is computer consulting for a U.S. company.  They would like to switch my relationship with them to their German office.

Questions:
3 - Is the activity of computer consulting required to charge TVA?  This question is for both an invoice to a U.S. company and an invoice to their German office.
4 - How should I label my invoices (both for the U.S. and for Germany)?

I am in contact with an accountant recommended by the bureau d’avocats with whom I have been working in creating the EURL.  The accountant has sent to me a list of the obligations of my EURL, including some that appear to need to be handled soon (i.e. by the end of the year).  These latter including Monthly TVA submissions (by 2019-Dec-21?), Monthly European Services submission (“DES”), and “Some punctual tax submissions”.

I have read elsewhere on your site that you recommend at least three quotes from accountants before selecting one.  Partly for this reason I don’t intend to engage an accountant immediately.  I will thus need to be able to do any initial required submissions myself.

Question:
5 - What submissions will I need to do myself before engaging an accountant?
6 - Is ‘impots.gouv.fr’ the appropriate portal for handling these submissions myself?  Will it be clear what needs to be done and how to do it?  If not, where should I turn for clarification?

I attempted a validation of my TVA number through the site ‘http://ec.europa.eu/taxation_customs/vies’.  The indicated result was that my TVA number is not valid for cross-border transactions within the E.U.

Question:
7 - What does it mean for a TVA number to not be valid for cross-border transactions?  What may I need to do about it?
8 - I did look at the answer to the questions mentioned in the message, which recommended the following web site: ‘FR: http://vosdroits.service-public.fr/professionnels-entreprises/F23570.xhtml’.  Is this the appropriate approach to correcting whatever problems may exist?
9 - In addition, other questions among the above mention a ‘TVA recapitulative statement’.  Is this something that I will need to understand and submit?