Cameras and lences

That's an old dilema dating way back to the film era.

You found a good and serious salesman. I realy think that his advice is very good.

No lense can do a good job as both a telephoto and a macro photo. As you said that you are ready do do some serious photography, and have outgrown your actual camera. That some of it is macrophotography, some more general use, and some nature, wild life, photos.

Usualy, zooms objectives need to do several compromises. This can lead to distortion when you are aproaching the limits of the zooming range, or are taking close shots.

I personaly think that you'll be beter with a body that can accept a veriety of objectives specialised to the various tasks. Those objectives will surely give you far beter performance and image quality than an 18x zoom, or any zoom, except, maybe, the very best zooms at exorbitant prices.

I'd go for:
A macro objective, possibly with some macro photo adaptors.
A good telephoto. Be sure to get a good tripod.
A mid range objective for ordinary use. The macro adaptors can be used with this one.
A general use zoom, with a moderate range, for when you can't bring several objectives with you and can't foresee your needs.
Keep your actual camera as a backup, or for situations where you don't want to risk your new camera.