Want to buy and sell resale hdb without loan - possible?

Hi I would like to sell my 4room hdb and buy a 5room hdb

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1. May I know if I should buy or sell 1st? How long usually is the process from putting up the flat for sale to selling it? Or how long usually is the process from actual viewing of flat to purchasing it?
2. Can someone also enlighten me on the following scenario too:

My current 4room is valued at about $550k and the 5room in the area we are looking at is about $700k

We have paid our mortgage in full some years back

My hubby and I have a combi cpf oa of $100k (after leaving 20k in each of our account) and I'm willing to fork out another 60k cash

We will also be able to get a subsidy grant of $30k for staying near parents

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My question is

A. Judging from the finances is there high chance we will be able to fully pay for the flat without having to take up a loan? Or are there hidden costs I have yet to consider? How do property agent commission work btw? I only know something along the line that it's 1% or more?

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B. Can anyone recommend some good blogs out there that I can read up on buying and selling of HDB? I can't seem to find much info online

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Thank you!