Some students do more than 1 module at a time, but it depends what else you do. At brick uni students are full time, so although they take 120 credits that's generally all they do - they might have a part time job, but it's generally 8-20 hours.
If you're working full time and have a family then that will take up a lot of your time. If you're intending to work 40 hours a week and study 40 hours a week, that only leaves 32 hours after sleep - and that's for travelling, cooking, eating, bathing etc. It is possible study 120 credits and work full time but you have to be really good at time management and be prepared to not do much else.
If your degree still does February starts this makes things easier, as you'll be doing one module October -June and one module February-October. But the OU have stopped offering as many February modules. It's also generally easier to double up on the level 1 and 2 modules and spread out the 3's.
How are your maths skills? You need to be really comfortable with the basics, as a lot of that is assumed you know - there will be tables to read etc.
You don't need a science A Level, so you'll be fine. You might need to put in a bit more effort at times to understand things but it will all be explained.
I didn't do the whole degree, but did take some of the modules as part of my degree in social sciences. It was interesting so although it was difficult it was easy to find motivation. You do need to keep on top of the work, though.