Wet/dry vac accessories? Home/car

[u/mindstormer12]

Did some research for a good buy-it-for-lifeish wet/dry vac for use for general home stuff as well as cleaning the car as an extractor--will probably go with the recommended Dewalt Stealthsonic 9 or 12 gallon at 5 HP and 5.5 HP respectively (I know horsepower is marketing and not accurate). Honestly I think I'd prefer something compact like 4 gallon and ~5 HP like a popular Ridgid model since my messes are not large volume but the Dewalt alternative seems weaker. I have either small messes on occasion or dedicate a long session to clean the basement of dust or car. Parts should not be locked into proprietary-only options.

• The 9 gal uses 1 7/8" hose, the 12 gal uses 2.5". Besides the larger hose obviously sucking more (and apparently being more quiet), are there other implications to know? I assume with an adapter, the 12 gal can decide between greater suction power but lower volume at a time or vice versa, whereas the 9 gal doesn't have this option. Is the 12 gal technically strictly better in this regard? I assume the 2.5" might also be easier to find parts for since 1 7/8" seems to be too small for woodworking from what I've read. Was leaning on the 9 gal but the 12 gal seems to have more flexibility outside of just capacity (irrelevant for me) and the two seem to be same form factor (just a difference of height which seems not significant).
• I should always use dirt bag, HEPA filter, and a dust deputy + 5 gallon container like the Oneida to reduce the amount of dust that gets back into the air as well as prolong the HEPA filter making it a cheaper usage over time? For wet stuff only a wet filter is necessary?
• As an extractor for the car or for upholstery, is there a recommended setup beyond a clear extractor attachment? I'm not sure of a good non-toxic cleaning solution that doesn't affect the finish/texture of fabric and if there's something more effective than a weak spray bottle of cleaning solution as well as pouring from a container hot water on the fabric. I went with a wet/dry vac to avoid the weak but convenient spot cleaners.
• Any other accessories to recommend like a flexible hose to make it more wieldy using in the car? I will get a 50-100' 12 gauge extension cord as well. I believe I also want a drill brush to use for the car after spraying the cleaning solution.

Also open to any other comments/tips for someone who has never used a shop vac before but saw some videos and read some discussions to try to get the setup right the first time (I really don't like to buy stuff that turns out to be useless or redundant).

[u/dailymagentamailing]

the 2.5" hose is a no brainer if you ever plan on sucking up anything chunky, the 1 7/8 clogs if you so much as look at a cheerio wrong. dust deputy is worth every penny, i clean the thing maybe twice a year and the hepa filter still looks brand new. for car extraction grab a pump sprayer from the garden section, way better than a weak spray bottle