Disclaimer: this is a general knowledge and not tax advice. You should seek professionals before making any financial and tax decision.
A.
It depends on someone circumstances and would need more information.
Generally it makes no differences if shares sold are held less than 12 months (don't have discount on capital gain)
Time frame on keeping records
(1) Share investors keep records until the share is sold (can be 5 year, 10 years or even 40 years!) and additional 5 or 10 years afterwards by law
(2) share traders keep records for 2 years (share trading business if total gross sales less than 2 millions a year)
Ease on reporting
(1) share investors may have more complication in calculation with factoring capital gains tax (long gain,short gain and CGT loss)
(2) share trader need 4 things, total financial year sales, total financial year buy, share holding@ 30/6 in actual cost methods and market value methods. Pretty much it is = give accountant the broker reports
Tax effective is significant when
(1) share investor will be benefit if having lot of long term gain ( hold more than 12 months).
(2) share trader will be benefit if having more loss which could offset other income.
P.S.: tax law do not allow cherry picking - can't pick and choose as trader a year, investor another year.
B.
Both investors and trader can claim these expenses, just under different area in tax return.
One advantage of a share trader (with total sales less than 2 million a year) is able to write off depreciable asset immediately if it is less than $20,000 (please discuss this with your accountant as I cannot provide financial advice).
An individual investor can only write off asset that cost less than $300.
The above could change tax outcome you raised in Question A.
