Without work authorisation you are not legally permitted to work in Thailand. A tourist visa does not provide work authorisation. You're risking penalty payment, deportation and worst case jail.
ad (1) High risk especially for prolonged stay in Thailand and regular 'visa runs' abroad. There has been increasing scrutiny and crack downs on visa violations recently. During the pandemic there was more flexibility, this is now being rolled back.
ad (2) If you stay more than 180 days in total in any calendar year (= tax year) in Thailand then you are deemed a tax resident. If you bring income into Thailand in the same calendar (= tax) year in which it is earned then you are liable to pay income tax in Thailand. Enforcement varies but it is a risk, especially combined with the lack of work authorisation and regular 'visa runs'. There is also permanent establishment risk for your employer if you work in Thailand for prolonged periods. That means your employer may need to pay corporate tax in Thailand.
Thailand last year launched a new Long Term Resident visa with a sub-category "Work from Thailand Professional" which provides work authorisation, 5 + 5 years visa and income tax exemption. Requirement is a certain minimum annual income level and some other specifics e.g. size and type of employer company.