tell me what you think - my first grow

Personally i have had bad luck with digital timers.

Also you should draw a sketch of the whole setup and make sure you have enough room for everything.

 

if you can afford it, go with 6 inch hood/fans. 4 inch is pretty small and i don't even know if you can get a 4 inch vented hood anymore. plus if you decide to upgrade to say a 1000 watt ballast, 4 inches won't cool very well.
make sure the bulbs you get are compatible with an electronic ballast, not all are. very good idea to get everything you need to finish before you start! kudos!

 

Those T5's should be more than enough for early veg stage, do you know what watt the T5's are?

As for switching to a 400w HPS, that again depends. If you have a spectrum enhanced HPS bulb you could switch when ever you like, aslong as you keep it in 18/6 or 24/0. Alot of people prefer to keep them under flouros or T5's up until flowering/late stage of veg.

Im not an expert by any means though so i might not be 100% right.

Good luck with your grow

 

Is this your 1st hydro grow or 1st grow?

I thought you had to do about 10 soil grows before you switch to hydro but goodluck

 

If I did my math right, your grow area is a hair under 4.5sq. ft., and 400W is WAY too high for that area and will cook your plants. You want to plan for +- 50W / sq. ft. to your plant canopy, so your grow area would be better suited to a 250W HPS setup. 400W is better suited to an 8 or 9 sq. ft. area. Expand your grow footprint or downsize your light.
Either way, also go with a Metal Halide conversion bulb that will run in your HPS ballast (or get a switchable ballast). This is SO MUCH faster on veg. than T5's or CFL's. I can veg. a freshly rooted cutting to 16" in 3 to 3.5 weeks under a 400W MH conversion bulb. Your 2ft. T-5 single is fine to root maybe a dozen cuttings, but veg-ing under that will take like 50 or 60 years(LOL).
Can filter 33 - aren't those built for a 6" fan / duct?
175cfm fan would be OK for passive room ventilation, but will NOT push the Can33 carbon scrubber. If I remember my specs for that scrubber, it needs like 450-600 CFM into the filter.
Scrap the digital timer - a grounded analog time at HomeDepot is like $8 and I've never had one fail. Running a lamp only, that's all you'll ever need.
GH Waterfarm 4 gal. or build your own? You can certainly build your own for the cost of a good dual-outlet aquarium air pump, some 6" net pots, 12" airstones, and one or two Rubbermaid or sterilite tubs. Look on this forum for "bubblers", very simple and effective as an entry to hydro.
Hydro Vs dirt - that a matter of preference, but IMHO hydro can be even more forgiving that dirt grows. You can't over-water, and unless you let your nutrient dry up you can't under-water. Con's for a home made bubbler setup - harder to check pH and change your nutrients. Best way is to have an extra bottom container, mix new nutes in it, pick the top off the old one and move it to the new container (don't forget to move the airstone too!!!).
Stay away from drip systems; for beginners the emitters are prone to clog.
Stay away from pure aeroponics setups; clogging and potential pump problems until you are more experienced.
Graduate to an ebb and flow table and you'll probably never leave hydro again. Simple, easy to set up timers, not messy (no run-off to deal with), and generally rock solid reliable. Replace your pump impeller ever 3-6months and you should never have a problem. Disconnect your pump hose from the table, plug it into a garden hose, turn on the pump, and you can manually evacuate your grow tub for nute changes as needed.
Now, go do it!!!!
Hope this helps.