@Dave264
I think, because this is a small business, that the income is claimed from Jan 1 to Dec 31 each year, as it will be claimed as personal income - so would follow your personal tax year. Unless you've incorporated...in which case it would be claimed for whatever fiscal year your corporation has set up.
The 30k threshold regarding GST/HST is strictly for business income, so no need to collect it if (for example) your gross earnings from ABB were $29,500 in 2018 and you also earned employment income, dividend income, or capital gains in excess of that.
Check with an accountant, obvs, but that's how I do it (as an unincorporated biz) and my accountant hasn't kicked.
Cheers,
Jen