Help needed to create a community site

Hi,

I had actually managed to create what I consider to be a community site with many modules to provide features I see on many similar sites. I was largely satisfied with my customized box_cleanslate theme and the site on a whole & looking forward to launching it.

I am currently using the following modules:

ACL, Forum Access, Front Page,
Audio,

ALL Core optional except book, legacy, locale, & ping,

Currency,Currency API,
Event,
Image, image gallery, Javascript tools (collapsiblock, javascript tools, tabs)

Advanced contact, archive, auto time zone, bookmark us, contact link, classified ads, F.A.Q, forward, greybox, xml Sitemap, Guestbook, Ip to country, login tobbogan, node images, page array, panels, pathauto, persistent login, poormanscron, postcard, printable, pdfview, recipe, service links, signup, site map, spam, token, update status, upload preview, url icon, extended user notifications, user protect, webform, weight

Smileys, captcha (captcha, capture image)

Syndication
jQuery Update,
External links
Video (Video, video upload)
Views (Views, Bonus audio playlist, Bonus summary + full view, Views RSS, Views UI)

Voting API
JRating

Disabled but desirable – Invite, Mass contact, Notify, Organic groups, OG Forums

I started experimenting with 4.7.3, then to 5.1 & recently updated to 5.2.
With the first 2 versions, I actually had many more modules, as I was experimenting with them to see what they have to offer. I never had any debilitating errors, like memory related inspite of those many dozen modules.
Multiple php-related problems came up, during a time some major server updates + transfer where taking place, including memory errors (one being told to increase memory & a while later a blank site). In that time, I used the prescribed solutions for solving memory related problems, like setting memory in settings.php. but they did not help, apparently UNTIL the server updates were completed, so I suppose at that time the problem was on the server which had to be reconfigured.

More recently after changing to 5.2 I have had some persistent problems with the error below coming up, when I try to set user access & creating new blocks. I abandoned a site when I kept having these problems & later a totally blank site (the memory increase in settings.php up to 60M) not helping.
I started anew using my customized theme & used the same modules.

I first enabled all, but when it came to setting user access, after reaching some point this error, which i was trying to avoid popped up again:

Warning: Unknown: failed to open stream: Permission denied in Unknown on line 0

Warning: Cannot modify header information - headers already sent in Unknown on line 0

When it does appear, the only way to save any user access settings OR new blocks is only possible after I disable a number of modules!
That can end up being an endless circle.
The fact is I have not been able to get the site to what it was before & in spite of getting rid of many many unused or dispensable modules, which however caused NO PROBLEM AT ALL in 4.73 & in 5.1 in spite of them being enabled & being able to create blocks & se user access with no problem at all.

This disabling of modules also has the effect of affecting the placement of new content on the front page in chronological order. I'm not sure what exactly triggers this, but new content stops being added at the front & is placed somewhere inside - not even appended to the first content.
If I disable all modules (or I think core modules) & re-enable them, the order is restored BUT new content is again added somewhere in the middle & not on the first page, EVEN IF for the concerned content, the settings are that it be published + being promoted to front page.

At the moment I am stuck & very discouraged, because these errors keep coming and unlike errors I got in the past, this one above seems set to stay. ... If I continue removing more modules, where is the limit without having to re-think the content?
From what I have seen, removing 5, 6, 7, 8 modules will not help much.

Assuming the modules listed above are too many, why where they & many more I deleted working before with no errors? I had for example several OG related modules installed, Acidfree, & lots more. Now I cant even activate a much smaller number or create the number of blocks (mostly for menu items) I had before!

Anyway, I'd appreciate some ideas of what to do, including alternative module combinations (even if the modules are much fewer), that would help me achieve as much of the current functionality as possible.
The community site has news, forums & users submit different types of content, including via the recipe module, different types of self-made content types and as you can see, photos, audio & video.

I would be grateful for any suggestions.

Regards