These are two complex issues that don't have easy solutions with the amount of information you proved.

1) GST - you need to go through the setup of the GST Taxes tab, Tax Code tab and Tax Code Details dialog to see what might be wrong.  Off the top of my head, I can't figure out why purchases would credit the liability account.  Therefore the best option is to review the settings.  If you feel they are correct, please post an image of each of the screens I mentioned.

2) Reconciliation - if you have done the reconciliations manually for a while and feel that the bank balance in the Sage 50 company file is correct, then you should be able to enter the period end like Oct 31/23 reconcile everything since the last reconciliation.  However, if you do not wish to do this, get a backup copy of your company file for reference in the future if needed, then don't just reset an individual reconciliation, reset the entire module and start over with the last reconciliation you did or with the first one of the fiscal year if you wish to have a full year available in the file.  To reset the whole module, select the bank account in the Chart of Accounts and open the ledger.  Select the Reconciliation and Deposits tab and uncheck the Save Transactions for Account Reconciliation check box.  Then hit the Save button on the toolbar.  Answer the prompt to confirm.  Then recheck the box and close the ledger and restart the bank rec using the Account Reconciliation module and the month's report from the month before the one you wish to start up in Sage 50.