Your front fork isn't going to snap for the kind of use you are describing. Ebike DIY discussion groups are littered with pictures of snapped forks and the cause is largely well known: The use of high powered motors coupled to suspension forks (they break without warning even when torque arms are used). Generally its accepted not to exceed a 500w motor on any suspension fork, and to be sure to use at least one torque arm on the thing (two is better). If you are doing a 350w motor, its likely going to be 25-35Nm and that is well under any limits - provided you install it smart (i.e. torque arms).
Front hub motors are pretty common on suspension forks in the EU (the ebike I rented just a few days ago in Amsterdam had one), but thats because they are limited by law to 250w ... at low power levels you have no issue - and they are PAS-only. No throttle. We here in the US would rather eat ground glass than use such a low power motor hence the universal shying away from them.
If on the other hand you are installing to a solid fork, you have nothing to worry about period at this power level although you always should use at least one torque arm. A solid, steel fork is by far the preferred solution. I've been using 80Nm, 750w fat motors on solid front forks for years and thousands of miles without issue, although they are part of a 2wd solution so the front fork is not pulling on its own. Even on a steel fork, I wouldn't put one on its own on a big, heavy fat bike. But for a low power bike, now having spent the day riding one and realizing its not the bugaboo (traction) its made out to be, a front motor is ideal for a basic city bike.
