Woot, Got a DS5 for 40$, So hello and checking in. =)

I would definitely Recommend starting here to get some background information for the S5. Link to Everything you need to know

There is not a Honeycomb version, only Froyo and Gingerbread (I don't consider eclair useful day top day). It all depends on what you want to use it for. There are different flavors of ROMs out, and each one is designed to do different things, like Gaming, Stability, CM7, MIUI, Long Battery life, etc.

In my opinion it is best to start with the basics and then try all of them or a few of them to find out what you like and don't like about each one.

Streak 5 is really good for daily tasks you throw at it, provided that you at least root it and remove all the bloatwares, maybe use custom launcher, custom kernel might not be preferable cause some basic functions may not be working.

I've moved on to XPERIA arc S late last year, but I still help with settings/tweak for the Streak 5 --- I gave mine for my nephew, he mostly uses it to play games (as much as his father allows), and Streak 5 is quite good at it, newer HD games might not run, or require tweaks to run, but most games on the Play Store would not be difficult for it to handle.

The only rom worth trying other than official rom is CM7. it offers many useful functions.

The best official rom is probably the only 2.3.3 rom. But it consumes more battery than the 2.2 rom.

My Dell Streak Story

nice score for $40!
I know how you feel. I got my first Streak 5 about 2 years ago on ebay for $73 because the guy lived out of town and no post, only pickup. He also listed it as Dell M01M tablet and not in phone or tablet section. Came with no charger or cables and seller couldn't tell me if it even turns on. Took a gamble and drove 2 hours each way to pickup. Didn't have a chance to get a usb cable to try it before pickup, so I butchered a lithium-ion camera battery charger and wedged 2 bare wires in the battery contacts and charged it from the ciggy lighter socket in the car! After a few minutes, I put the rear cover on and pushed the power button and got a warm fuzzy feeling as the Dell logo appeared on the screen. After a while, donut 1.6 fired up and Stage UI appeared and I was the happiest person in the world!
I am typing this post on that first streak right now!
2 years later, I now have 3.5 x Dell Streak 5 (.5 is one with smashed lcd for parts). 3 of them I paid less than $100 each. I paid $150 for one that came with a lot of accessories. I love this thing. It is without doubt, one of, if not THE best value android devices on the second hand market!
I am currently working on making a mounting frame to turn one into a carputer to fit in double DIN slot in the dash.
Out of all the roms for the DS5, I like the CM7 the most. I have a Galaxy S2 with ICS rooted without mods and it doesn't really offer anything useful that CM7 doesn't cover. A lot of the customisations in CM7 like the notification panel mods are way more flexible than ICS. I don't feel any need for ICS with CM7.
I switch between using the streak and galaxy s2 as main phone.
Got my girlfriend finally using a streak as her phone because she needs screen size to use a web page to book rostered hours for work and as she put it "using a normal phone to do it is crap!" She also prefers the bigger screen for playing Angry Birds!
Would go a galaxy note but at about 7 times the average price I paid for each streak, I'll stick with the streak!

Have you considered a S7 for a double din mount?

I hear it's exactly the size of a double din if you remove the case and side bumpers (or something to that degree).

A S5 would leave a lot of unused space, unless that's the plan so you can put something else with it.

carputer

I don't really want to strip the casing to mount it. I am trying to do a neat mount that only shows the screen and capacitive buttons and front camera. This means I need room in the frame to hide the dock connector and a button mechanism to press the volume/power/camera buttons which will be covered by the frame.
The other benefit of using the S5 over the S7 is the FM radio capability of the S5. S7 doesn't have the FM tuner.