Whatever you do, find a comfortable position for playing your bass where you can access all of the notes on your neck and keep both wrists strait at all times. Find some strings that feel comfortable for your fingers, and sound good to your ear.
Whatever level of calluses you experience from 4 months of playing, and whatever side effects you get from that will surely diminish after just a little more time. I remember feeling like my finger tips had been dipped in wax, and it felt weird to touch everything. I remember a friend talking some really disgustingly sappy B.S. about girls and being able to feel a girls soft skin when he held her hand, and thats why he played with a pick
so he could at least feel things with his right hand finger tips. *barf* You see, the truth is, thats just a stage and youll move past it. Give it some more time, and yes youll have calluses on your fingers, but you wont feel them or notice them at all.
When you get to the well established callus stage, where you dont even notice them anymore, you wont really get blisters anymore either youll only ever get hot spots. Be on the lookout for that.
A hot spot is basically a blister under a callus, but it doesnt bubble up like a blister because its under a hard callus. Youll feel a finger tip starting to get real warm, and if you dont lay off, itll feel hot
and when you look closely later, youll have a little tiny white spot there. It might be barely noticeable, but just like with a blister in soft sensitive skin, once a hot spot happens, the skin on top of it is doomed. With a blister, its going to bubble, pop, peel, and completely heal over within a couple of weeks. With a hot spot, because the skin on top is a callus, its going to take months. But trust me, once you feel the hot spot come on, and you can see it later, that callus is going to shed a layer of skin. Itll be over the course of the next few months. It will not bubble up into a blister. If you leave it a alone, it shouldnt really bother you at all. Itll just be like the callus gets really hard for a few weeks where you had the hot spot, then it cracks for a few weeks, not deep at all, just in the top layer of the callus which is all dead skin anyway, and then you get little hang skin things that hang from the cracking callus, and get really dry and flake off. Never ever pick at them.
When you pick at the little bits of skin to pull them off, they may run deeper, and THAT will cause pain, little dents, little divots, etc in your finger tips as they heal. Your finger tips will take a real long time to become round again once they heal to a healthy callus with a divot or string groove in it because you pulled at bits of skin while it was healing. A string groove or divot in your callused finger tip can really inhibit your playing. You dont want a groove in your finger tip, it makes it super hard to fret any note without fretting out. You may want to lightly file your finger tips with an emery board to help get the little dry bits of skin off, but like mom said - dont pick at it.
If you are playing long and hard enough to get to the stage where you are playing through your calluses, you are probably playing hard in other ways too so, again, make sure both wrists are strait so you dont catch the carpeted tunnel syndrome, make sure you wear ear plugs so you dont go deaf, and do not pick at your fingers when they shed a layer because you insisted on playing till you got a hot spot - and rock out!