1. workshop likes you to change to biggest possible cos means more money for them. few points to note:
- 16" both rims and tyres are more expensive than 15". for typical replica rims, difference could be about $20-$30 per rim. for tyres it could be about $40-$50 per tyre. add them all up x4 and you'll know the difference.
- typical 16" tyre profile for Fit is either 205/45/r16 or 205/50/r16. 15" typical is 195/50/r15 or 195/55/r15. with a wider profile, you get slightly better stability but will become slightly more sluggish (especially with the Fit's small engine) and getting slightly poorer fuel consumption, sometimes very subtle and not readily noticeable. you can get a 195/50/r16 profile but typical replica rim width for 16" is 7", which is quite wide for a 195. can put no problem, but may not look as nice la.
- Fit/Jazz fender space allowance sucks. stock 16" rim is only a 6" width rim with a 185/55/r16 tyre. offset is quite a whopping +53 which you'll almost never find outside. and this rim is almost just flushed with the fender (for the front. rear is ok). stock 15" rim is a 5.5" width rim with a 175/65/r15. offset is +45 which is also quite hard to find. and this is almost perfectly flushed with the fender. both tyre size are odd sizes and hard to find, which means limited tyre choices. and anything thicker/wider than that, your front wheels will protrude out of the fender, which looks fugly. but that's more of a cosmetic issue. you may be ok with it. but at least i can't stand it.

do note that typical offset for replica 15" is +40 6.5J and 16" is +38 to +40 7J. subtract from the +45 and +53 (in mm) respectively and you'll know how much the wheel will shift outwards. and not only that, the wider tyres will just worsen it. 16" looks horrible, to me. UNLESS you go do cambering to say 1 to 1.2 degrees, but that will set you back by another high 100s.
so there you go... if you are ok with the cosmetic issue (front wheel protrude out), by all means but i would suggest 15" at most, and with a 195/55/r15 instead of a 195/50/r15. 55-profile is slightly thicker and more comfortable if you are already used to your 14" thick tyre comfort. also, if your Fit is the 1.3 non-skyroof version, i believe your suspension is different. it's slightly higher. if you put a 195/50/r15, actually it's quite thin and end up you have a very big gap between your tyre and fender. doesn't look nice. ok, again, cosmetic issue.
also note that by changing to even 15", you may notice slightly more sluggish compared to your 14", and fuel consumption may be slightly poorer.
for tyres, if you are looking for comfort, i suggest michelin xm2. if want better performance tyres, then michelin ps3 or bridgestone re002.
2. i've not much experience with aftermarket wipers as i always buy the original wiper rubber and use back the original frame.