My first ever grow -

Does anybody fancy helping a girl in need? This is my first grow, however I've had two failed attempts!

I haven't actually started again yet because I'd really like to get it right this time! So...

Im in the UK, therefore I've chosen bio bizz soil, canna products, 1.2x1.2m 2m tall complete tent set up.
Ive started my plants off so far in the propagator, which was easy enough, but I'm never getting dry soil! Once I've planted seed and done the initial water how long after that till the next watering? Is there a rule of thumb I can follow? How many plants do you think I could get in my tent comfortably? I'd like more than one just incase one does go later on in process? I've got 400w Philips bulb that apparently does all 3 stages of development, should I buy a separate bulb for veg/flower? When do I start feeding nutes? And is it a good idea to use ferlite or clay balls as drainage at bottom of plant pots as my soil never seems to get dry! So far I was using coco soil but trying bio bizz this time!

The one thing I'm not confident with is terminology but...my tent has an av temp of 25-29c the rH is 23% on average, is this way too low? Do I need to buy a humidifier?
When I close my tent the temp shoots up to 33c! Do I need more fans? Currently have 4 x15"!

Buggared two crops of critical mass so far so would really like to get this next lot right! Starting with northern lights, heard its the most basic of plants to grow.! Would like some hazes eventually and kush! Please any advice or Critisicm needed!!

Also the best pH tester? I've got a really basic set and I think that's my main problem is the soil pH!

the humidity dome on the propagator keeps all the moisture in so they really dont dry out until they sprout and start using water. once you have a sprout remove the dome and keep a close eye on your sprout, it will dry out quick if your humidity is low. you dont have to worry so much about low humidity as high humidity (mold) just keep an eye and make sure its getting enough water.

your 400w bulb, is it MH or HPS? If it is HPS youre ok to run it start to finish.

You are probably ok to use plain water for a few weeks but i dont have much experience in soil so maybe someone else can comment.

Your 4 fans, are they oscillating fans? in most setups (especially tents) you need an inline fan to extract the hot air from the top of your tent and it will pull in cool fresh air from the intake flaps at the bottom.

They have soil pH probes that you stick in the dirt, i've never used one but i hear they aren't real accurate. i think most soil growers collect the run off from their pots and test that with a pH pen. i bought a hanna combo meter and the pH stopped working on it but the ppm and temp still works fine. for pH i use a $15 yellow milwaukee one. cheap and works fine and stays pretty accurate.

Thank you! It's a hps but I was told if you grew for extra 1-2 weeks with that bulb it grew the same results. The only problem I'm having at the minute is the transfer from windowsill to tent, i soak the soil and they go in but if I put the light where it should be they burn, too far away and they just turn yellow and crispy! I can't work out what I'm doing or if I'm over/under watering

how high is the light above the soil? you might want to consider using a few CFLs until youre out of the seedling stage. these HPS lights are just too darn hot for little sprouts.

i do hydro but i do have houseplants in soil that we usually "love to death" from overwatering. the gf and i each water the houseplants and soon they are falling over dying. but we are getting better at that. last night we transplanted a root bound lilly that was drooping pretty hard. and im just gonna let her water all the houseplant from here on! I believe a rule of thumb is to stick your finger in the pot and if it is moist 2 knucles down it doesnt need water.

How often are you watering and have your sprouts got their first set of true leaves yet?