Help with selling & buying houses please.

[cornishpasty]

We've been thinking about moving for a while now but i just don't know where to begin. I've worked out how much we can afford and i've found a good fixed rate mortgage deal (actually with our current lender).
Do we need to get a written mortgage in principle from them?
Can anyone give me any idea of solicitors costs when selling and buying - is it a good idea to ring around and get some prices?
Do you have to pay any costs upfront or can they all be paid on completion. We have no real savings and would struggle to pay many costs now. We would be borrowing extra to cover all costs so would have funds available then.
Any other tips or suggestions on this stressful process would be gratefully received.
TIA

cornish - its not necessary to get a written offer from them initially as long as you know they will be good for the money when the time comes. Solicitors costs do vary greatly and are usually on a sliding scale - the fees for purchasing being greater as there is more work to do plus the disbursements (search fees etc). You will need to pay your disbursements up front usually but costs are taken from proceeds of sale or money held in the account.

Is worth having a ring around for solicitor...although even better would be if you know anyone who has bought or sold, from whom you could get a recommendation. Solicitors vary in terms of how 'quick' they are to proceed with transactions. As with most things, a good recommendation is worth its weight. If you know/have a good agent, they will be able to tell you the good solicitors in the area. Personally, I would avoid internet based solicitors/agents....but I am sure there are people out there who have had a fine experience with them. Search fees etc which are required up front are generally a couple of hundred pounds at the most. In general, EA's will take the selling fee on completion. With regard to mortgage, only when you have agreed a sale and found somewhere to buy will the agent want details of the mortgage lender. Just keep in regular contact with your lender to make sure they are still good for the deal, in principal. (as other contributor has said)
I do some work pt for an EA and have worked for conveyancing Sol so if you want any other advice, just ask.

You will need to pay approx. 10% deposit at exchange. If you are exchanging on your current house at the same time, your buyer will have to pay a deposit too, you can use this as at least some of your own deposit.