Hi @Shijun,
A warm welcome to the Bunnings Workshop community and thank you for your question.
If you want to retain the rugged texture and character of the reclaimed wood, you can skip sanding entirely but be aware that rougher wood may absorb the finish unevenly, creating a more rustic look.
At a minimum, you should give the timber a good scrub with soapy water and a scrubbing brush to remove any dirt or oils that can affect absorption.
To maintain as much of the character of the timber, I'd suggest using a clear oil over a varnish. Varnish will create a film over the timber, whereas oil will penetrate it and maintain the natural feel. Considering you'd like the rustic nature to be a feature of the piece, I think oil is a much better option for this reason.
My suggestion would be either Cabot's Clear Danish Oil or Gilly's 100% Pure Tung Oil. They are both clear oils that will cause minimal colour change while still protecting and enhancing the natural look of the timber.
Once you've built the table, please remember to share your project, it would be fantastic to see what you create.
Let me know if you have any further questions along the way.
Jacob
