[member=179432]ojfarmer[/member]
Firstly, re your Q2, I have not considered a timer and cannot offer any really useful comment: however, I'm sure I've seen various UK offerings (albeit have not paid much attention to). Whether for mains water or gravity fed systems and then whether mains fed or battery powered electrically I couldn't say.
As to your Q1, I'm struggling to give a definitive answer about pressures/flows.
Your greenhouse situation will be very different to my sloping field situation. [To note: my willow sapling spacings are presently 3' along rows and 4' between rows - I will interplant at 2' between rows in due course. Also, if I had thought I would actually need to irrigate my sapling plots routinely I would have run my inter-plot service lanes across the slope and set my rows down the slope, but I did the opposite: therefore my irrigation sections run off a feeder spine running down-slope with rows running across-slope.]
However, for what it's worth ...
I have gone through various irrigation section set-ups (testing as I go) and the farther I move sections down the hill, the greater the water-head/pressure obviously. I started out assuming 13mm hose was the way to go, but am now more inclined (for my purposes) towards maximising 5mm hose usage.
My moveable irrigation sections are set up with a down-hill spine feeding either 5 or 10 across-hill rows - sometimes feeding 30' rows in a comb arrangement and sometimes feeding 15' rows in a spine and ribs arrangement. I continue to experiment, but at the moment everything sort-of works.
To further ease relocation of my original, wholly 13mm hose sections, I have now separated the 13mm hose spine from the 13mm hose rows and use 5mm hose to re-connect the 13mm spine to each 13mm row - that shouldn't work should it? - but it does, albeit with row hoses taking a little extra to time to be primed across a 50-plant section.
Other irrigation sections:
I also run sections with 5 or 10 rows of 5mm hose (with 15' rows) off a 13mm spine.
I also have a set-up for apple plots that is wholly 5mm in 25-plant irrigation sections: I connect 2x 25 plant sections to a split hose-pipe feed to irrigate 50 plants at a time (it could manage more without doubt).
And all gravity fed using standard 1/2" garden hose to connect irri' sections to IBCs (since I've chosen to not move IBCs) as I move irri' sections down the hill and with plenty of standard hose-pipe connectors in between (with their restricting 9-10mm bore).
Optimised? - no. Works? - well enough for me.
I attach a pic of a Liquid Lever set-up in (I believe) Africa that they sent to me. I believe it gives an indication of how a 13mm set-up (at least) might be used for annual crop beds - I noted the doubled-up feed (at bottom-right of pic) to another bed beyond.
Of course I have to say, oj', that your situation is very different to mine. As much as I like the components and flexibility of the Liquid Lever system, you might want to talk to them first about your longer term need to supply 4x greenhouses