I have been directly involved in many planning applications . . . objecting, supporting, discussing, deciding . . .
There are lots of issues which planners are not allowed to take into account, such as reduction in value of your property, disturbance during the construction process, etc. It’s worth trying to exclude this sort of stuff from your letter, as it undermines the other valid points you raise.
As others have said, try to relate your objections to planning policy. The planning officer should point you in the right direction for this.
Is it an application which only affects the immediate neighbours, or does it have a wider implications? Are other local residents in favour of this development? One of your local councillors MAY be able to help you, but avoid contacting someone who sits on the planning committee, as you may compromise their position.
Another important point is will the decision be made by the committee, or by the planning officer (“delegated decision”)?
Good luck . . . and remember there’s no logic in the planning process!