Two choices
1. Get solicitor now. Get them working on taking up your Deeds and preparing contracts so that , if and when, it all starts happening, you are ready to go.
2. Wait until it is quite clear that everything is ready to move before getting onto solicitor.
All solicitors are advising clients not to get their hopes up. My own view is that a deal is not done until the money is in the bank and any deal, contracts or no contracts, can collapse at any stage given (a) many vendors and purchasers naivety ( still) and (b) the banks increasing unwillingness to lend to anyone.
In addition, most vendors will clearly say that, actually, they will only sell if they can buy at the same time which is making a lot of transactions even harder to complete.
You don't need a solicitor to make your offer.
As regards other interested parties, the house will be sold to the highest bidder if they are in a position to complete ( i.e. they have their funds organised and do not need to sell their own). If a lower bidder is in a position to complete, they are in a much stronger position.
mf