[TYPO3-english] Advice needed for creating a new version of an existing website

[Mattia B]

Hi, I'm very new with Typo3.

I've been hired to build the new version of a website currently based on typo3 4.2.x.
All functionality currently implemented should also be available in the new website.
My job is to a) add some functionality and b) remake the website graphics.

I was evaluating the option of:
- reusing the current codebase
- update typo3 (and extensions) to 6.2
- implement new functionality
- remake the templates

I'm encountering a lot of issues in upgrading.
Particularly the fact that the website is currently depending on old extensions (templavoilà, dam, ..).

My questions are:
- would it be better starting from scratch? (current website has a lot of data which should be reimported/remapped somehow)
- is 6.2 a good version to go with or is it already getting old?
- in the case of reusing part of the current codebase is it feasible to switch the template engine and what engine would you suggest?

Any help greatly appreciated!