I've recently obtained a 13 inch Bridgesii with roots which is my first cactus. The potting mix I used was about 45% perlite 40% cactus potting soil, 10% desert sand, and 5% bone meal. After researching on here and elsewhere about indoor growth I also got a grow tent and a 1000W all spectrum LED as I was planning on growing my cacti indoors at first, but changed my mind and decided to let them outside as much as possible now. I live in an area where half of the summer or more is complete overcast and not very warm (it can get in the low 60s at night) so what I've been doing so far is taking them outside on clear sunny days and having them inside with the indoor lighting otherwise. I'm wondering if anyone thinks this would be bad to continue or if it is fine to have a mix of indoor lighting and natural lighting some days, and if any problems would arise from this. It may be important to note that windows are not an option in this situation.

Also I would like some advice on winterizing them, should I just leave them in the dark inside the grow tent from October/November - Summer with almost no water? I've read lots of advice that says attempting to continue growth in the winter causes skinny growth or etiolation.

Hopefully I'm not going about it too terribly wrong, any advice or comments are appreciated.

Your bridgesii will be fine outside overnight in the summer. Just put it outside when the risk of frost is past - and if there's an unexpected cold snap, wrap it up in a thick blanket. Save the lighting tent for early spring and late autumn if you want to stretch your growing season. In winter, keep dry and protect from frost.

Taking your cactus outside only when the weather's sunny puts it at risk of sunburn.

Be careful when using fertilizer on your cactus. During the active growing phase it will respond well to tomato feed - diluted to half strength - every couple of weeks, at least once the bonemeal is depleted. It sounds like your compost mix wouldn't need additional perlite, considering it was a cactus mix in the first place. If you wanted to add something to improve drainage, I'd suggest lava chippings.

Once your cactus gets established you won't want to be carrying it around every day - and if you get a collection started you'll soon be thinking of moving somewhere where the cacti can stay outside as much as possible! Best wait until you at least have a few window sills at your disposal before expanding your collection.