You have the almost eternal problem of which mount. And you will always get told the biggest, in a way makes sense, but from experience there is more then that.
The EQ6-R is nice, will last you for years (ever?) and is plain heavy/big.
Using the Skywatcher options:
EQ3 - way too underweight for real AP.
EQ35M - Unfortunately looks the same in being too lightweight.
EQ5 - More solid looking mount, one that many here have started with.
HEQ5 - Fairly good solid mount, will last you for at least a number of years.
EQ6-R - probably the one to have, would save you gym membership or do you have a fork lift truck.
The problem is I bought an HEQ5, good mount. Left it in the car for about 8 weeks before I plucked up the courage to get it out. Even in many bits it was a struggle. Just heavy. And that was in component bits.
I went and bought an EQ5. OK smaller, not so good. It does one thing the HEQ5 doesn't. It gets used.
So yes buy the biggest, but it could be useless if it sits inside.
Now will say the HEQ5 is likely the better mount for starting, but one group many years back all used EQ5's. BUT their expectations were realistic. And what they did was realistic. Seems these days expectations exceed equipment. And people keep adding more and more, and want to do less and less themselves.
If you go above EQ5 then get organised - some means of transporting the mount items around, not you simply lugging them.
The iOptron mounts seem light in physical weight, but high in cost. And these days all mounts seem prone to death and problems. In iOptron you are likely looking at their 40 rated mount, the 25 might be OK but it seems a bit of a nightmare to live with. Although few screams of pain from owners recently.
If you want to simply go collect say 60 second images, OSC type, with a small scope 60-70-80 ED refractor type. Say 120-150 exposures (3-4 hours collection) and do it unguided then an EQ5 will get you by.
If you want to join in the longest exposure competition so guiding system, use a 100-120 triplet, mono camera and filters then you will need the EQ6-R (the HEQ5 might squeeze in).
So a huge amount comes down to what it is you want to do, and I mean what you really want to do. I know someone that produces excellent images, they also have £30,000 of equipment.