Exasperating Container Gardening Chaos

Hi.
been gardening just a lil over 3 months, container gardening mostly, zone 11.

Ive had some friends give me zinnias and allamanda young seedlings and tried to grow them (since my efforts at growing from seeds have been ..oh well)

These are my concerns. They were doing fine - exposed in a well aerated/ventilated area, full direct sun, water them when soil dries out.

1. Allamanda. Ive managed to grow them but they dont seem to flower and bloom. Ive used a bloom booster (15-30-15, 1x a week) a month after i got them established but nothing. I was advised to prune them which I did very minimally but still nothing. Any advice on what im doing wrong?

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2. Zinnias. I thought these were easy from seeds but after 3 months have nothing to show. These are seedling Ive managed to establish for a month and half, but things are turning bad i think

the leaves are turning brown or have a withered look about them. After which, Ive also noticed some spots of mildew. Ive used a cinnamon fine mist spray on them 2x a week/ and/or ground cinnamon powder on the leaves as well so they kinda stick to the affected leaves). Some of the leaves tips have turned brown as well.

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3. Prior to these issues, ive used a bloom booster (npk 15-30-15) once a week on them. A friend suggested a fish emulsion with npk of 2:1:25) - is this a good npk ratio? also does fish emulsion prevent flowering as I read in some blogs.

4. Finally, so far the only plants Ive managed to grow (fingers crossed) are the mexican sunflowers. But Ive noticed some of the lot have marked yellow veins along the leaves. Some neighbors say it is diseased (pest) others say its alright. being an amateur,i really dont know if it is a cause for alarm.

View image: photo yellowing veins

Your inputs and advice will be greatly appreciated. Thank you!

I'm having trouble picturing your set up (and your pictures are really tiny and don't help much). You said well ventilated, which sounds like enclosed, we don't bother saying that plants in the ground are "well ventilated" (though of course they are). But then you said, full direct sun. Those two don't quite seem to go together; it is hard to have full direct sun in an enclosed space.
1) allemanda. How big are the plants? How big are the pots? What kind of potting soil? Concentrated bloom booster fert every week sounds like too much. What has your weather been like? You said zone 11 (where is that, Key West?), so I'm assuming hot, but hot and wet? hot and dry?
Allemanda is a tropical. It likes well drained sandy soil, but not to dry out much. In my experience tropicals really benefit from being misted as well as watered.
Super K Fulvate- Fulvic Acid, Humic Acid, Bulk Fertilizer