The guidelines suggest either a ban of up to 28 days or 4-6 points. The overwhelming likelihood is six points. The Single Justice will not disqualify you in your absence. In the unlikely even that disqualification is considered, your case will be adjourned to a hearing in the normal Magistrates’ Court and you will be asked to attend.
You will also face a fine of a week’s net income (reduced by a third for your guilty plea), a surcharge of 40% of that fine and around £95 prosecution costs.
Sentencing for speeding is quite prescriptive and there is rarely anything that can be said which will significantly influence the outcome. There is absolutely no point in engaging a solicitor.
In summary, plead guilty and do not ask for a personal hearing which you can attend (unless you particularly fancy a day out).