Advice for an Astro Photography Setup [ THE OTA - THE TUBE] - Choosing a NEWTONIAN reflector 8" F5 (perhaps F4) FOR photometry

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This is a branch of another post which makes an intro about my project and needs:

https://www.aavso.org/advice-astro-photography-setup-doing-science

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 IMPORTANT: 

In this post, I will  mark the questions I WOULD like to be answered with this emoticon  and italics, to make a little easier to identify my questions .. Of course, you are invited in all comments you like,but this are the questions I would made if this were a conversation.

Why did I choose a Newtonian??

APERTURE -> Looking for the biggest newtonian the mount can support and my budget could afford gives me more photons for stellar astrophotography (NOT INTERESTED IN EXTENDED OBJECTS ASTROPHOTOGRAPHY LIKE NEBULA), and  . I know about COMA aberration, so My choice would be 8" - F5 but I can read another options. My CMOS camera choice (based on Iis a very small chip so I think the COMA is not a problem. I know there are good coma correctors so I can improve my setup in the future with a very portable accessory (but not very cheap). RC are better in image but the price per photon is expensive. About the collimation in newtonian, I think I will be capable. I KNOW is a must to do collimation...  But I can bear that, if there is an OTA with the screws to do this easily. If I use the central part of the newtonian F5 with a small sensor, I think I will be fine... What do you think?

PROs:

• A lot of photons.
• Cheap
• A lot of options in the market
• I don't care much about coma aberration . because I am not making artistic pretty pictures...
• Coma problems can be fixed somewhat afterwards
• I don't have condensation like in the SC

CONS

• Long tube: problems with wind
• Many of them are heavy and need expensive or sturdy mounts.
• Somewhat difficult to put in equilibrium over the mount

I want to buy a tube and a mount. But I want a reflector for these goals:

MAIN GOALS: MAKING SCIENCE

• Stellar astro photometry /astrophotography of Variable Stars, Supernovae, and Near Objects (NEO) asteroids, and other stellar objects
• Astrometry or measurement of  position, of asteroids , NEOs, 
• Occultation observation of stars by asteroids
• Observations of far - faint comets
• Other transient events
• Precise photometry of exoplanet transits
• Measurement of orbits of faint moons of outer system planets
• Measurement of proper motion of fast moving stars
• Parallax experiments

IMPORTANT! WHAT ARE NOT MY GOALS! .... (but I can do very rare if the gear allow to, btw)

• Color artistic / cosmetic photography
• Nebula photography
• Direct observation by a viewfinder
• Planetary
• Solar
• Near big comets

I want to make astro photography with photometry with a IMX178 based camera like the QHY 178M Monochrome Astronomy Camera # QHY178M, the ZWO ASI178MM or an Orion StarShoot G4 Monochrome

 A NON-HEAVY TUBE with A LESS EXPENSIVE MOUNT.  Is a good idea to accomplish the budget?

STEEL OR ALUMINIUM WHAT TO CHOOSE?

SIDENOTE: SIZE!!!

Ok, I am between two diameter sizes, 6" and 8". I will try to fix my budget with a 8" option. BUT the mount usually is more expensive and heavy so It is a but difficult to find a kit.... Can you help me to find the option...  

 SPECIFIC OPTIONS (in not very specific order)

Orion 203mm f/4.9 Reflector Telescope Optical Tube Assembly
250USD https://www.telescope.com/Orion-203mm-f49-Reflector-Telescope-Optical-Tube-Assembly/p/9788.uts
PROS: is very lightweight, 2" focuser. Weight under 16.5lbs (will be this weight true????)
BONUS PRO: Is one of the most lightweight options, so I can buy a cheaper and less expensive mount.
CONS: it doesn’t seem a high quality product. Perhaps a generic mirror. It is a main stream budget product as far as I know.. I have doubts if I can colímate this

GSO 8" f/5 Newtonian Reflector Telescope - Steel OTA (White) # GS630
419USD https://agenaastro.com/gso-8in-f5-newtonian-reflector-ota.html

PROS: IF the info on the site of GSO is correct, GSO seem a very qood quality maker. So I will have a quality OTA. 2" focuser, good for collimation. FAN for cool air inside the tube
CONS: HEAVY. I need a bigger mount,because is over the 20lbs. Second hand market will be more difficult with a not so know brand

sidenote: If i cannot afford a mount for this last one, I can choose the 6" F4 option: https://agenaastro.com/gso-6in-f4-newtonian-imaging-reflector-ota.html, or the F5 62 GSO option: https://agenaastro.com/gso-6in-f5-newtonian-reflector-ota-focuser-upgrade.html

CELESTRON 203mm F5 tube WITHOUT the ADVANCED VX MOUNT KIT. or WITHOUT IT (much dificulty to find because I think is not in catalogue now, can you know if this OTA is in Celestron catalogue and I can ask for it separately of the mount)
Around USD350

• Link with the MOUNT https://www.highpointscientific.com/celestron-advanced-vx-series-8-quot-newtonian-go-to-telescope-32062    
• Link without the MOUNT https://telescopes.net/store/celestron-c8-n-advanced-newtonian-ota.html

PROS: I think is a good price for the kit. And is a good brand. Good reference, many users. Good warranty and aftersales support, am i right?

Lightweight : If I can buy the OTA not the mount, I can put it in and less expensive mount

Is fitted perfectly to the mount. Is designed for it. I like the mount but is a heavy one.

CONS: Is not a specific astrograph. It has Big boxes for the shipping. I think I will have quite problems with the transport. Easy aftermarket value: celestron is a well known brand
NOT very much info about the quality of the tube: Is a begginer telescope for astrophoto. So i have doubts about the quality compared with the GSOs. I think is a clone of the ORION OTA I mentioned above, because is an aluminium tube in the same weight around 14-15 lbs. .Do you know more about this OTA and the quality compared with GSO? 
Is not a double speed eyepiece. This can be improved afterwards but this focuser are usually built in budget telescope what do you think? 

I am open to other brands of 8" telescopes, but I think GSO is a good choice.

What other options are available to me?

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This is a branch of another post which makes an intro about my project and needs:

https://www.aavso.org/advice-astro-photography-setup-doing-science

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