Gem, your plan sounds practical and feasible. If you've worked out that 7 months is what you can afford, then enjoy that time with your baby. Other people (including family) are not in your exact position, so their experience and advice was correct for them, but maybe not you.
In some sort of ideal world, the absolute gold standard would be for a baby to get to spend something like the first 2 years with their mother. In this real and imperfect world, not many people (including me) can do that, so we work something out. Babies are adaptable and the older they get, the easier it is for them to cope away from their mother. If you have family to care for him/her, then statistically in terms of baby satisfaction you have the second best option. So don't feel any guilt or worry over it.
From experience, it is easier to leave your baby with someone else if they are used to feeding from a bottle. This is not something to immediately worry about as you can't know how well breastfeeding will go or how long it will last until you and the baby try it. So that's a thing to work out post-birth.
What you could do now is talk to your family to see if they are willing to provide childcare, whether they want paying, how holidays will work and if they will look after the baby in your style or theirs. I've seen some posts on Mumsnet from parents who have problems with childcare from family members, so reading through those could give you an idea of potential stumbling blocks. Chatting about it now could avoid awkward situations later.
On a lighter note, my daughter was notably happier as a stranger-wary baby when getting cuddles from my sister (who looks like me) or FIL (who looks like my husband). She used to study them intently, in a kind of 'you look awfully familiar' way.